The car drove along the road from point A to point B = 27 km at a certain speed. Back it went along a different road

The car drove along the road from point A to point B = 27 km at a certain speed. Back it went along a different road = 20 km. From the way back the car arrived 10 minutes earlier, although the speed on the way back was reduced by 3 km / h. Find the speed of the car on the road from point A to point B.

Let the speed of the car from point A to point B be equal to x km / h, and the time spent on the road is equal to t hours. We compose equations based on the initial data:
x * t = 27; t = 27 / x;
(t-10/60) * (x-3) = 20;
Substitute the value from the first equation into the second:
(27 / x-1/6) * (x-3) = 20; 27-27 * 3 / x-x * 1/6 + 1/2 = 20;
– (x ^ 2) / 6 + x * 15 / 2-81 = 0;
x ^ 2-45 * x + 486 = 0; (we solve the quadratic equation)
D = 2025-1944 = 81;
x1 = (45 + 9) / 2 = 27;
x2 = (45-9) / 2 = 18;
We got two solutions to the equation, both of them are correct.
Answer: the speed of the car on the road from point A to point B is 27 km / h or 18 km / h.