Date range & grouped averages

I am a TOTAL newb but I can't get this to work and really need it to:

I have a simple fact table (Calls) with two dimensions (Time, Sender). I need to get a sender total number of calls grouped by day-of-week and the avg number of calls on each day (how many calls on an average Monday) within a certain time period.

    <Dimension name="sender">
        <Hierarchy hasAll="true" primaryKey="id">
            <Table name="actor"/>
            <Level name="sender" column="actorUID" uniqueMembers="true"/>
        </Hierarchy>
    </Dimension>

    <Dimension name="time" type="TimeDimension" caption="Times">
        <Hierarchy hasAll="true" primaryKey="id" name="complete">
            <Table name="time"/>
            <Level name="aYear" column="year" type="Numeric" uniqueMembers="true" levelType="TimeYears"/>
            <Level name="aMonth" column="month"  uniqueMembers="false" levelType="TimeMonths"/>
            <Level name="aQuarter" column="quarter"  uniqueMembers="false" levelType="TimeQuarters"/>
            <Level name="aWeek" column="week" type="Numeric" uniqueMembers="false" levelType="TimeWeeks"/>
            <Level name="aDay" column="day" uniqueMembers="false" levelType="TimeDays"/>
            <Level name="aHour" column="hour" uniqueMembers="false" type="Numeric" levelType="TimeHours"/>
            <Level name="aTicks" column="ticks"  uniqueMembers="true" levelType="TimeSeconds"/>
        </Hierarchy>
        <Hierarchy hasAll="true" name="ByQuarter" primaryKey="id">
            <Table name="time"/>
            <Level name="qQuarter" column="quarter"  uniqueMembers="true" levelType="TimeQuarters"/>
        </Hierarchy>
        <Hierarchy hasAll="true" name="ByMonth" primaryKey="id">
            <Table name="time"/>
            <Level name="mMonth" column="month"  uniqueMembers="true" levelType="TimeMonths"/>
        </Hierarchy>
        <Hierarchy hasAll="true" name="ByDay" primaryKey="id">
            <Table name="time"/>
            <Level name="dDay" column="day"  uniqueMembers="true" levelType="TimeDays"/>
        </Hierarchy>
        <Hierarchy hasAll="true" name="ByHour" primaryKey="id">
            <Table name="time"/>
            <Level name="hHour" column="hour"  uniqueMembers="true" levelType="TimeHours"/>
        </Hierarchy>
        <Hierarchy hasAll="true" name="ByTicks" primaryKey="id">
            <Table name="time"/>
            <Level name="tTicks" column="ticks"  uniqueMembers="true" type="Numeric"levelType="TimeSeconds"/>
        </Hierarchy>
    </Dimension>

    <Cube name="usage">
        <Table name="calls"/>

        <DimensionUsage name="Time" source="time" foreignKey="time_id"/>
        <DimensionUsage name="Sender" source="sender" foreignKey="sender_id"/>

        <Measure name="Count" column="id" aggregator="count" formatString="#,###">
            <CalculatedMemberProperty name="MEMBER_ORDINAL" value="1"/>
        </Measure>

    </Cube>

Can anybody point me in the right direction to write that MDX query?