I need helping finding out how to do this

Look at arnold's attempt to solve the equation for b: 3b = 12 b = 3 · 12 b = 36 describe the mistake that arnold made.

Icould really use some with this question.

Ke’ajah has a coupon for 1/3 off the regular price, t, of a tent. which expression represents the price of the tent using the coupon? select the two correct expressions. a. 1/3t b. 2/3t c. t - 1/3 d. t - 2/3 e. t - 1/3t f. t - 2/3t