Answer:
12t + 7y = x
or
5t + 770 = x
Explanation:
12t + 7y = x
t = number of hours he worked as a tutor
y = number of hours he worked as a waiter
x = the total amount of money he earned
t + y = 110
=> y = 110 - t
=> 12t + 7(110 - t) = x
=> 12t + 770 - 7t = x
=> 5t + 770 = x