To divide fractions, you use CCC: Copy Change Change rule. You copy the first fraction, change the sign to multiplication, and take the reciprocal of the second fraction.
7/15*5/3. Because 5 and 15 are diagonal from each other, they can be simplified by dividing 5 from each to get 1 and 3. 7/3*1/3. Your answer would be 7/9.