Lamar works as a tutor for $7 an hour and as a waiter for $8 an hour . this month he worked a combined total of 92 hours at his two jobs let t be the number of hours lamar worked as a tutor this month .write an expression for the combined total dollar amount he earned this month

t is the number of hours Lamar worked as a tutor 
We know that he worked for 92 hours total, so he worked 92-t hours as a waiter.

So his earnings are: 7t + 8(92-t) = 736 -t dollars

This expression seems logical as if Lamar worked 0 hours as a tutor and 92 as a waiter his earnings would be 8*92 = 736
If he worked as a tutor for 92 hours it would be 7*92= 644 
736-92= 644 
So our expression seems to be working.