Okay. So to answer this question, let’s find the LCM of both numbers, which means listing the numbers that a number can go into evenly.
3: 3, 6, 9, 12, 15, 18, 21, 24, 27
8: 8, 16, 24, 32, 40
When you look at both of them, you see that they both have a multiple of 23. So Marco will fill his car with gas and wash his car on the 24th day.