If you would like to know how much greater is the area of the broadcast region when the signal is relayed, you can calculate this using the following steps:
x% of 50 miles is 75 miles
x% * 50 = 75
x/100 * 50 = 75 /*100/50
x = 75 * 100 / 50
x = 150%
150% - 100% = 50%
The area of the broadcast region when the signal is relayed is 50% greater.