Devon’s teacher requires that students show each step in solving a problem. devon wrote the following when solving the equation x- 7 = 20: x -7 = 20 x -7 = 20 + 7 x = 27 the teacher said that devon’s work was not shown correctly. why? a) devon’s final answer should be 13 b) devon should have shown that he added 7 to both sides c) devon should have shown that he subtracted 7 from both sides d) devon should have shown that he added 7 to the left side only