The ratio of the number of basketballs to footballs to volleyballs is 6:5:7. If there are 4 more basketballs than footballs,

(a) How many each of the three kinds of balls are there?

Basketballs:

Footballs:

Volleyballs:

(b) If the price of a football is 15 dollars, how much money does the school need to buy these footballs, in dollars?