Answer:
39 inches
Explanation:
the triangle has all equal angles
this means it is equilateral and this also means all the sides are equal
so take 2 sides and set them equal to each other to find x
21 - x = x + 5
now solve
add x to both sides
21 = 2x + 5
subtract 5 to both sides
16 = 2x
divide everything by 2
8 = x
now flip it
x = 8
plug this is to one of the equations and multiply that by 3
8 + 5 = 13
13 * 3 = 39
that is the perimeter