perimeter of shaded = 15+15+15 = 45
perimeter of unshaded = 21+21+21 = 63
ratio from small to large = 45/63 = 5/7 = 0.714
since area is squared you need to square the ratio of the perimeter = 0.714^2 = 0.51
12. use 63/45 for scale of 1.4 then multiply 50 x 1.4 = 70
