Hi Abdi.

Let s = the speed of the car and t = the time it takes to drive 175 miles.

Then 175/s = t.

If the speed was 20 mph faster (that's s + 20), then the time would be one hour less (that's t - 1)

So 175 / (s + 20) = t - 1.

This gives you two equations with two unknowns, so you can solve it from here.

Look up simultaneous equations in our Quick Search if you need more help.

Cheers,
Stephen La Rocque.