#### Answer

$4y-y^2$

#### Work Step by Step

We start with the given expression: $y(4-y)$
To simplify an algebraic expression, we must eliminate any parentheses and combine like terms. To eliminate parentheses, we apply the distributive property: $4y-y*y$
We multiply $y*y$ to get $y^2$: $4y-y^2$
Since there are no like terms, the expression has been simplified.