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

D = a*t + b * (T-t)

Explanation:

In the example given, four variables are to be considered here,

How many dollars he makes per hour, same as how many dollars he makes as a waiter, How many hours he worked both as tutor and a waiter

Let define our variables

let a = the amount of dollars he makes per hour as a tutor

Let b = the amount of dollars he makes as a waiter

Let t = number of hours he worked as a tutor

Let T = the total hours combined he worked both jobs in a month

Therefore, T-t = number of hours left he worked as a waiter.

Then, D = total dollars Frank received this month in which is: D = a*t + b * (T-t)