Two cars simultaneously go on a 950-kilometer run. The first one travels at a speed 18 km / h

Two cars simultaneously go on a 950-kilometer run. The first one travels at a speed 18 km / h higher than the second, and arrives at the finish line 4 hours earlier than the second. Find the speed of the first car.

Let’s take the speed of the 1st car for x, then:
x-18 – speed of the second;
950 / x – travel time of the 1st;
950 / (x-18) – 2nd time.
Since the 1st came to the finish line 4 hours earlier, we get the equation:
950 / (x-18) -950 / x = 4
950x-950x + 18 * 950 = 4x (x-18)
4x (x-18) = 17100
x ^ 2-18x-4275 = 0
x12 = (18 + -√324-4 * (- 4275)) / 2 = (18 + -132) / 2
x = (18 + 132) / 2 = 75 km / h.
The second root of the equation is negative and has no physical meaning.