How does the 1/4 and 3/5 become 3 and 6 units respectively?

I don’t need a new answer. Just an explanation. Thank you!

Note that the starting point I used was 1 unit for A unsold and 2 units for B unsold.

For A, it was 1 unit at first, which can be used for total 4 units since it is 1/4

But for B, 2 units cannot be used to represent 3/5, so we need to split all the units by 3 for the simplest model. Then expand it to include baked, sold and unsold on the right side. This is the simplest way to use the same units to represent both A and B.

Thank you Dr G!

Thank you Mimosa! I won’t give up!