use unitary method
let cost of 5 box is 25 cents .
therefore cost of 1 box =25/5 cents =5 cents
and cost of 30 such boxes = 30 *(5) = 150 cents
total cost of x apples = b cents
therefore cost of one apples = b/x cents
now you can calculate cost of 2 apples or 9 apples or y apples
cost of y apples = yb/x cents