Ok I figured it out.

The ratio is 4 to 3 on width and height respectively. So I did 4^2+3^2 = 25 for the diagonal. 25 is already a "squared" and 54 is not. So square root of 25 is 5.

I then divided 54 by 5 to get the magic number 10.8.

width=10.8(4)=43.2

height=10.8(3)=32.4