Feather3, I like the way you did this, but you are not keeping the ratios the same by subtracting 4 from each side. When you subtract 4 from 19, you are reducing the 19" side by 21%. To keep the ratios the same, you need to reduce the 15" side by 21% also, which means subtracting about 3.15 (.21 x 15") from that side instead of 4.