Let the width of the shortboard is x and the width of the longboard is y.
Then, 3x = 4.5 + 2y.
Or, 3x - 2y = 4.5
If y = 11.25, then,
3x - 2(11.25) = 4.5
3x - 22.5 = 4.5
3x = 4.5 + 22.5
= 27
x = 9
Hence, one of the possible solution is width of the shortboard is 9 inches and the width of the longboard is 11.25 inches.