Answer: 48 per second.
Explanation:
First start by choosing a number. for example: 20. Then Sum The number 3 times 20 + 20 + 20 = 60. You need to get to 144 so I pass 20 and go to 30. 30 + 30 + 30 = 90. Lets pass and go to 40. 40 + 40 + 40 = 120. Its close. when Im close I Start summing 41, 42 and so on. 48 + 48 + 48 = 144. I reach to 144. So that means 48 is the answer.
Hope Is it correct!
-Mrs.Egg :3