part c and b arent clear but the answer to a is this:
if you want to find 40% of something, start with finding 10% then multiplying by 4 to get 40%. 10% of 24.99 is 2.49. 2.49 times four is 9.96. so thats 40% of 24.99.
to find the price, subtract 9.96 from 24.99.
you get $15.03