Vishal wants to burn at least 2,400 calories during his weekly workouts. He burns 400 calories per hour swimming and 600 calories per hour rollerblading. He decides to swim for 3 hours this week. How many hours must he rollerblade to reach his goal?

Let x be the number of hours Vishal swims and y be the number of hours he rollerblades.

Given that Vishal swims 3 hours, the number of hours spent rollerblading is represented by
.