Answer: 37. 5 minutes in total.
So someone else had gave the correct answer, but I thought it wasn’t clear enough so I hope this helps.
Explanation:
45 + 30 = 75.
But 75 cannot be a total of minutes... so therefore we divide 75 by 2
75 ÷ 2 = 37. 5
So it will take you and your friend a total of 37. 5 minutes to wash a car together.
Hope this helped