Solution:
Let t be the number of hours Mai works as a tutor.
Given that She earns $12 a hour as a tutor, this implies that for t number of hours, she will earn
[tex]\begin{gathered} \$12\times t \\ =\$\text{ 12t} \end{gathered}[/tex]For the month, she worked a combined total of 85 hours. This implies that
[tex]\begin{gathered} 85=t\text{ + (number of hours worked as a waitress) } \\ \Rightarrow nu\text{mber of hours worked as a waitress = (85-t) hours} \end{gathered}[/tex]Her total eranings for the month is expressed as
[tex]\text{Total earnings = 12(number of hours worked as a tutor)+7(number of hours worked as a waitress)}[/tex]Recall that she earnes $7 an hour while working as a waitress.
Thus, we have her combined total amount in dollars expressed as
[tex]\text{Total earned (in dollars)=12t+7(85-t)}[/tex]Hence, the expression is
[tex]\begin{gathered} \text{12t+7(85-t) } \\ \text{open parentheses} \\ \Rightarrow12t+595-7t \\ \text{collect like terms.} \\ \text{thus, the expression is simplied to be} \\ 5t+595 \end{gathered}[/tex]
