For this case what we should do is define variables:
x: time in minutes
y: number of clean cars
We then have the following equation:
y = (20/50) x
For 1 car we have:
1 = (20/50) x
Clearing x:
x = 50/20
x = 2.5 minutes
Answer:
It will take the machine to clean 1 car about:
x = 2.5 minutes
