Description: Learn how to evaluate an expression with variables using a technique called substitution (or "plugging in"). Created by Sal Khan and Monterey Institute for Technology and Education. The individual cost of participating in the raffle is given by the following expression: 5t plus 3, or 5 times t plus 3, where t represents the number of tickets someone purchases. So let's first take the situation where t is equal to 1. Then this expression right over here becomes 5 times 1.*Teacher Advisor is 100% free.