We have the following:
Bob's earnings can be calculated with the following equation
[tex]B=45+32.5x[/tex]where x is the number of hours, they tell us that he made a profit of $ 207.50, we replace and solve for x
[tex]\begin{gathered} 207.5=45+32.5x \\ 32.5x=207.5-45 \\ x=\frac{162.5}{32.5} \\ x=5 \end{gathered}[/tex]Therefore, Bob worked a total of 5 hours