Multiply 21-y (y+3) Multiplying Monomials and Binomials:

-y² - 3y + 21

Step-by-step explanation:

Our expression here is 21 - y (y + 3).

Let's focus on the parentheses part: y (y + 3). This is basically the same as writing y * (y + 3). We need to distribute out this parentheses. To do this, we multiply the outside term (y) by each of the inside terms (y and 3) and add those together:

y * (y + 3) = y * y + y * 3 = y² + 3y

Now, let's put that back into the original problem:

21 - y (y + 3)

21 - (y² + 3y)

21 - y² - 3y

The answer is thus - y² - 3y + 21.

~ an aesthetics lover