Answer: 165 ≤ t ≤ 225
Step-by-step explanation:
If he mowed the lawn exactly once, then 55 ≤ t ≤ 75 describes all the possible values of t. Basically t is between 55 and 75 inclusive of both endpoints.
Multiply each value by 3
55*3 = 165
75*3 = 225
That's how we end up with 165 ≤ t ≤ 225 to represent the possible span of time values where he mowed the grass three times. His fastest possible time is 165 minutes (2 hr, 45 min) and his slowest possible time is 225 minutes (3 hr, 45 min).