To evaluate the expression for a given point we need to use the value provided in place of the unkown variable, in this case it'd be "y" and "z". Doing this below we have:
[tex]\begin{gathered} f(y)\text{ = y + 9} \\ f(16)\text{ = 16 + 9 = 25} \end{gathered}[/tex]The second expression is:
[tex]\begin{gathered} f(z)\text{ = 11 - z} \\ f(4)\text{ = 11 -4 = 7} \end{gathered}[/tex]The third expression is:
[tex]\begin{gathered} f(y,z)\text{ = }\frac{y}{z} \\ f(16,4)\text{ = }\frac{16}{4}\text{ = 4} \end{gathered}[/tex]