Answer:
t+623
Explanation:
If t is the number of hours Ivan worked as a tutor this month, you can say that the number of hours that Ivan worked as a waiter would be the result of subtracting the amount of hours he worked as a tutor this month from the combined total of hours he worked, which is:
89-t
After this, you can say that the combined total dollar amount Ivan earned this month is the result of adding up what he earned as a tutor plus the amount he earned as a waiter which is equal to 89-t. So, you would have:
8t+7*(89-t)
=8t+623-7t
=t+623
This means that the expression for the combined total dollar amount he earned this month is: t+623