Q1. Determine how far is it from the ground to a GPS satellite directly from the overhead?
Q2. How long does it take light (or the radio waves) to go from a GPS satellite overhead to the ground?
Q3. Let’s state that the time measured in problem (2) was measured by the clocks on ground. What would that time is if measured by clocks on the GPS satellite rather?
(That is, apply whatever speedup/slowdown factor you got above).
Q4. Multiply the time in problem (3) by the speed of light to get a distance and compare it to the distance you had from problem (1). That provides you an idea of how far off your GPS measurements would be if you did not take into account special and general relativity.