Let x = length of the base
Then, 2x + 2 = length of the altitude
Area of triangle = ½(base)(altitude)
So, ½(x)(2x + 2) = 72
Simplify to get x2 + x - 72 = 0
(x + 9)(x - 8) = 0
x = -9 or x = 8
Since x can't be negative, x = 8
base = x = 8 cm
altitude = 2x + 2 = 18 cm