To solve this, you need to make the amount they built on Monday and the amount they built on Tuesday compatible with each other so you can add them together to subtract that amount from 4.
Start by multiplying 1/2 by 3, and 1/3 by 2.
This gives you 3/6 and 2/6. Now add them together:
3/6 + 2/6 = 5/6
Finally, subtract this amount from 4:
4 - 5/6 = 3 1/6 (19/6 works too)
Hope this helps! :)
