Question is incomplete. Here is the complete question.
A city employee paints curbs iin parking lots and replaces road signs. It takes 0.5 hour to paint a parking lot curb and 2.5 hours to replace a road sign. The function below can be used to find c, the number of parking lot curbs the employee paints when he replaces r road signs in a 40-hour workweek.

If the employee painted 20 curbs in one week, how many road signs did he replace that week?
a) 20 b) 30 c) 0 d) 12
Answer: d) 12
Explanation: In one week, the employee painted 20 curbs.
c is the number of curbs painted in one week, so: c = 20





r = 12
In one week, the employee replaced 12 road signs.