Like terms must have the same variables and those variables must have the same powers.
and
are like terms, because they both have
and they both have
.
and
are NOT like terms, because the powers no longer match.
In your example, do you have the same variables and do the variables have the same powers in both expressions?
28 / 8 = 3.5
20 x 3.5 = 70
20 men can chop down 70 trees
If 24 × 3 is 72
Then 12 × 3 is 36
So the answer is 36/72