Repeated percentage calculating question

Question

"In a town, 75% of the workers drive a car to work. During an environment-week, only 20% of the workers drove their cars to work. How large percentage of the workers that normally drive the car left their car at home during the environment-week?"

The correct answer should be 73% according to my book, but I cannot come to that answer. I know that I shouldn't do: $0.8*0.75$ (because that's the calculation if 80% of the 75% workers left their car at home). I simply cannot understand how to come up with the answer, so I'm really thankful if anyone can explain how to solve this problem!

Answer 1

$75\% - 20\% = 55\%$ of the total population left their car at home. As a percentage of the workers who usually take their car, this is $$\frac{55\%}{75\%} \cdot 100\% \approx 73\%$$

Answer 2

Say there are 100 workers. Usually 75 of them drive, but during environment week only 20 of them drive. Thus 55 of 75 drivers left their car at home. $55/75 \approx 0.73$.