What was the rate of interest?

Question

A man needed money to buy lawn equipment. He borrowed  $800. for eight months and paid $53.94 in interest. What was the rate of​ interest?

Answer 1

800(1 + r)^2/3 = 853.94

853.94/800 = (1 + r)^2/3

(853.94/800)^3/2 = 1 + r

r = (853.94/800)^3/2 - 1

r = 0.1

10%