Sam works as a tutor for $10 an hour and as a waiter for $7 an hour. This month, he worked a combined total of 91 hours at his two jobs. Let t be the number of hours Sam worked as a tutor this month.

Sam works as a tutor for $10 an hour and as a waiter for $7 an hour. This month, he worked a combined total of 91 hours at his two jobs. Let t be the number of hours Sam worked as a tutor this month. Write an expression for the combined total dollar amount he earned this month.