Question 265446
Let the speed of the slower car = x
Then the speed of the faster car = x+40
Given,while one travels 150 km, the other goes 350 km 
Time = distance/speed
150/x = 350/(x+40)
3/x = 7/(x+40)
3(x+40) = 7x
3x+120 = 7x
120 = 7x-3x
120 = 4x
4x = 120
x = 120/4
x = 30 km/h