Question 145975
You must square the ratio of perimeters in order to get the ratio of areas.  Therefore:
Ratio of Perimeters: 15/8
Ratio of Areas: 225/64
So, 225/64=100/x
Cross Multiply to get: 6400=225x
Divide by 225 and simplify to get: x=1600/57, which is approximately 
27.1 rounded to the nearest tenth