We need to find the LCM (Least Common Multiple) of 4 and 5.
Let's list out the multiples of 4 and 5:
4 - 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, ...
5 - 5, 10, 15, 20, 25, 30, 35, 40, 45, ...
We look at the multiples and see the common ones.
Common are 20 and 40.
The least?
Of course, 20.
So, the LCM of 4 and 5 is "20".
LCM(4, 5) = 20