So you have length l=legs and b=base the first perimeter is 2l+b=8.5 since there are 2 legs the second perimeter is 4l+b=15.5 since the legs are now 2l long instead of l subtract the top problem from the bottom problem (4l+b)-(2l+b)=15.5-8.5 2l=7 so l=3.5 if l=3.5 and 2l+b=8.5, 7+b=8.5, so b=1.5 check by plugging it into the second perimeter 4(3.5)+1.5=15.5-->14+1.5=15.5 it's correct yay!