To find out how much Frank earns for working 23 hours, you can multiply his hourly wage by the number of hours he worked:
\[ \text{Earnings} = \text{Hourly Wage} \times \text{Hours Worked} = 7.40 , \text{USD/hour} \times 23 , \text{hours} \]
Calculating that:
\[ 7.40 \times 23 = 170.20 \]
So, Frank earns $170.20 for working 23 hours.