The answer is 5 units I believe
2 times the cube root of 8x+9=5
divide both sides by 2
cube root of 8x+9=2.5
cube everybody (put to 3rd power)
8x+9=2.5^3
8x+9=15.625
minus 9 both sides
8x=6.625
divie both sides by 8
x=0.828125
Hi there friend, your answer for perimeter is 18.
I’ve included a graph below to help explain why but basically if you count the squares, each side measures 4 1/2 units so if you multiply 4 1/2 units by 4(the number of sides) you get 18.
I guess it's 42
Hope it's helpful for you