Sales price is $81, gross profit is 170% of cost, what is the value of gross profit? Choose the correct choice:
A) 32  B) 33  C) 39  D) 40  E) 51

Rationale: "cost + profit = sales cost + ( 170 / 100 ) cost = 81 cost = 30 profit = 81 - 30 = 51 answer ( e )"
Answer: E