Question

Which expression is equal to 4y?

y + 3

y2 + y2

3y + 1

y + y + y + y

Answer 1

y + y + y + y = 4y

you can think of it as
1y + 1y + 1y + 1y = (1+1+1+1)y = 4y

or as

(1 yak) + (1 yak) + (1 yak) + (1 yak) = 4 yaks

Answer 2

y + 3 would NOT turn into 4y because the two terms (y and 3) are NOT like terms

you can't say y+3 = 4y or you can't say y+3 = 4. You just leave it as y+3 and you can't simplify any further. The same applies to the other expressions except for the last one