When querying a $3-$dimensional database, assume one of the dimensions is called $$Location$$ and it shows different cities in the U$.$S$.,$ and the other dimensions are Product Category $($laptop$,$ PC$,$ phone,..$)$ and Month $($January$,$ February,...$),$ and the cells show sales volume for the intersection of these dimensions. Assume the user wants to find out the sales volumes in Philadelphia and in April. The OLAP function that serves this purpose is: