Subtract the sum of(8m-7n+6p)and(-3m-4-p)from the sum of (2m+4-3p)and(-m-n-p)

Julie goes to the sports store and spends $40.50 before tax. she buys a pair of shorts for $21.75 and 3 pairs of socks that each cost the same amount. how much does each pair of socks cost? $$