A truck travels the distance between two cities in 30 hours. If a truck and a passenger car leave these cities

A truck travels the distance between two cities in 30 hours. If a truck and a passenger car leave these cities at the same time towards each other, they will meet in 12 hours. How many hours does a passenger car travel between cities?

Let us denote the distance between cities S.
Let us take as x the time of passage of the distance S by the second machine then:
S / 30 speed of the first car;
S / x – speed of the second car;
S / 30 + S / x – the speed of approach as the cars are moving towards
Since they will meet in 12 hours, we get the equation:
S / 30 + S / x = S / 12
reducing the resulting equation by S:
1/30 + 1 / x = 1/12
1 / x = 1 / 12-1 / 30 = 30 / 360-12 / 360 = 18/360 = 2/40 = 1/20
x = 20.