Evaluate each expression if r= -3, s= 4, and t= -7.
a) 252 + r - t
b) 3(-t)2

Sanderson is having trouble with his assignment. his shown work is as follows: − 3 7 7 3 = − 3 7 × 7 3 = − 21 21 = −1 however, his answer does not match the answer that his teacher gives him. complete the description of sanderson's mistake. find the correct answer.