Question 886172
Let 3x = length of the base

So the length of each leg is (2/3)(3x)=2x

perimeter= 2x+2x+3x = 42 cm
7x = 42 cm
x = 6 cm

base = 3x = 3(6cm) = 18 cm
leg = 2x = 2(6cm) = 12 cm