Hey there!
To write an expression to represent this:
We know that the four red plates each have 5 muffins, and 4 x 5 = 20.
So we can say 20 + 2y is the expression, because we add 20 to the muffins on the two yellow plates.
The number of muffins on each yellow plate is represented by the variable y.
If each yellow plate has 8 muffins, so y = 8, the expression will look like this:
20 + 2(8)
Multiply 2 x 8.
20 + 16
Add 20 + 16.
36
Belle baked 36 muffins total.
Hope this helps!