Two cars are driving toward each other with the speeds 30 mph and 40 mph respectively. if the distance between them are 350 miles, after how many hours they will meet?

Time = Distance /  speed

Let X = number of hours.

Car 1 is driving 30 miles per hour for X hours, so you have  30x.
Car 2 is driving 40 miles per hour for x hours, so you have 40x.

30x +40x = 70x

70x = 350 miles
x = 350 / 70
x = 5

They will meet in 5 hours