Answer:
Since this is an equilateral triangle, we know that all sides have the same length so: x + 1 + x + 1 + x + 1 = 12 (the perimeter)
x + 1 + x + 1 + x + 1 = 12
3x + 3 = 12
-3 -3
3x = 9
3x/3 = 9/3
x = 3, substitute 3 into the side lengths
3 + 1 = 4
4 is the value of each side length.