all the sides of the triangle are the same because this is equilateral. this means:
(21 - x) = (2x - 3) = (x + 5)
Let's take (x+5) and (2x - 3)
x + 5 = 2x - 3 subtract x from both sides
5 = x -3 add 3 to both sides
8 = x you can rearrange this to x=8
Now it's the fun part! SUBSTITUTION! :D (sarcasm)
BUT WAIT Remember, all of the sides are equal to one another! That means we only have to solve for one side!
Let's do the top side. 21 - 8 = 13
Since there are 3 sides in a triangle, we can easily multiply the 13 by 3
13 x 3 = 39 The perimeter is 39 inches
