Select the proper placement for parentheses to speed up the addition for the expression 2 + 9 + 8 + 1 a. (1 + 2) + (9 + 8) b. (8 + 9) + (2 + 1) c. (9 + 2) + (8 + 1) d. (8 + 2) + (9 + 1)

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.