To find the value of x, we will have to set the perimeters equal.
(2x+4)*4 would be P for the square and (2x+8)*3 would be P for the triangle.
We have to set these equal and solve for x.
(2x+4)*4=(2x+8)*3
8X+16=6x+24
-6x -16 -6x -16
2x=8
x=4
Now we plug x=4 in for each perimeter.
Square: 2(4)+5=13
Triangle: 2(4)+8=16