set two of the sides equal to one another:
8x - 20 = 4x + 18
4x = 38
x = 38/4
x = 19/2 or 9.5
now that we know x, plug it back in to find the side lengths:
4(9.5)+ 18 = 38 + 18 = 56
that is your side length
since it’s equilateral, the perimeter is equal to
56 x 3
final answer: 168
hope this helps:)
