The ratio of length to width is:
ratio = 48 inches / 30 inches = 1.6
This ratio must be similar to that of the other school banner, therefore the width of that is:
width = 15 / 1.6 = 9.375 inches
The areas are:
A1 = 48 inches * 30 inches = 1440 square inches
A2 = 15 inches * 9.375 inches = 140.625 square inches
So the ratio of the area is:
A1 / A2 = 1440 / 140.625
A1 / A2 = 10.24