http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/Pythag/pythag.html#section6.1
shows that the area/perimeter ratio can be pretty much anything..
A 6,8,10 island has A/P of 24/24 = 1
A similar shaped 12,16,20 island has A/P of 96/48 = 2 etc
Looks like a dodgy question...
Living on the coast
George and Martha are living on Pythag Island. Not surprisingly, it is in the shape of a right-angled triangle, and each side is an integral number of miles (under one hundred) long. Martha noticed that the area of the island (expressed in square miles) was equal to an exact multiple of its perimeter (expressed in miles). George was trying to work out that multiple, but gave up: “Please write down the appropriate digit.” he said. “Impossible!” said Martha.
What are the lengths of the coasts?