16+20

Let's solve the expression step by step:

When $y = 4$, the given expression is $y^2 + 5y$.

Substitute $y = 4$ into the expression:

$4^2 + 5(4)$

Now calculate:

1. $4^2 = 16$
2. $5(4) = 20$

So, the expression becomes:

$16 + 20 = 36$

Thus, the value of $y^2 + 5y$ when $y = 4$ is $36$.

Would you like more details or have any questions about the steps? Here are 5 related questions:

1. What is the value of $y^2 + 5y$ when $y = -3$?
2. How would the expression change if it was $y^2 - 5y$?
3. What happens if $y$ is a fraction or decimal value?
4. Can you express $y^2 + 5y$ in factored form?
5. What is the solution to $y^2 + 5y = 0$?

Tip: When substituting values into an equation, always follow the order of operations (exponents, then multiplication, then addition).