A plumber charges $45 an hour. If the plumber charged Luke $180, how many hours did she work?

To find out how many hours the plumber worked, you can use the formula:

\[
\text{Total charge} = \text{Hourly rate} \times \text{Number of hours}
\]

In this case, the total charge is $180 and the hourly rate is $45. Plugging these values into the formula gives:

\[
180 = 45 \times \text{Number of hours}
\]

To find the number of hours, divide both sides by $45:

\[
\text{Number of hours} = \frac{180}{45} = 4
\]

Thus, the plumber worked for **4 hours**.