Final answer:
To calculate the combined total dollar amount Austin earned this month, you can use the expression 9t + 8(105 - t), where t represents the number of hours he worked as a tutor.
Step-by-step explanation:
The combined total dollar amount Austin earned this month can be calculated by multiplying the number of hours he worked as a tutor, t, by the rate of pay for tutoring, $9 per hour, and adding it to the product of the number of hours he worked as a waiter, (105 - t), by the rate of pay for waitering, $8 per hour.
The expression for the combined total dollar amount Austin earned this month is: 9t + 8(105 - t)
By solving this expression, you can find the actual amount Austin earned.