91Ó°ÊÓ

To add two numbers with similar signs, add their absolute values and keep the similar sign with the resulting number.

To add two numbers with opposite signs, subtract the absolute value of smaller number from absolute value of larger number and keep the sign of larger number with the resulting number.

If two positive numbers 2 and 3 are being added, then the resulting sum will be $2+3=5$, which is positive as well.

And if two negative numbers $-2$ and $-3$ are being added, then the resulting sum will be $\left(-2\right)+\left(-3\right)=-5$, which is negative as well.

The difference of the numbers $7-3=4$ is positive because the larger number is positive.

And the difference of the numbers $3-7=-4$ is negative because the larger number is negative.

To evaluate the expression $y+9$, substitute 16 for y in the given expression and add the numbers as shown below,

$\begin{array}{c}y+9=16+9\\ =25\end{array}$

Thus, the value of the expression is25.