Question

Tina has 3 stacks of 5 cds on each of 3 shelves. How many cds does she have?

Answer 1

She has a total of 45 CDS. 

One Shelf Have 15 Cds 
 Multiply 15 x 3 and you have 45 CDs total

Answer 2

Equation
(5 x 3) x 3=
15 x 3= 45

Answer is 45 cds

Think about it like this.
There are 3 stacks of 5 on one shelf. So there is 15 in total on 1 shelf. Since each shelf has the same number of CDs answer is 45. 15+ 15 + 15