Since there are 3 sides in a triangle, and each side increased by 6, that means that the perimeter increased by 18 inches. Down below, I did 3x because there are 3 sides in a triangle.
(This is the equation you'd want to do to get the answer)
The answer is D. First, it is the segment addition postulate because the two segments make up the whole. Second, it's substitution because you are substituting EF + FG for FH.
