We have the next information
Julie bought
15 baseballs
x softballs
the total is $90 each ball cost $5
we can have the next equation for the total cost
15(5)+x(5)=90
we need to isolate the x in order to know how many softballs Julie bought
75+5x=90
5x=90-75
5x=15
x=15/5
x=3
Julie bought 3 softballs
