The perimeter of a triangle is the sum of its 3 sides.
x + (3x - 1) + (4x + 2) = 81...combine like terms
8x + 1 = 81...subtract 1 from both sides
8x = 81 - 1
8x = 80 ...divide both sides by 8
x = 80/8
x = 10
so ur 3 sides are :
x = 10
3x - 1 = 3(10) - 1 = 30 - 1 = 29
4x + 2 = 4(10) + 2 = 40 + 2 = 42