Lee wants to increase the number of minutes he exercises each week. If he increase his current time by a factor of three he will exercises for 144 minutes a week.

This means that Lee would multiply the current number of minutes he currently exercises by a factor if 3 to get 144 minutes of exercise.

Explanation: The few factors of 3 that can be applied here are: 2, or 3. That is to say that if Lee is used to exercising for 72 minutes, if wanted to change that to 144 minutes he'd multiply 72 by 2. Also if he was used to exercise for 48 minutes, he could multiply that by 3.

These variations are used because we weren't told the specific number of minutes he exercises for.