To find the value of a function in a given point we have to plug the value in the function and make the operations.
In this case we have the function
[tex]f(x)=2x+7[/tex]Then:
[tex]f(3)=2(3)+7=6+7=13[/tex]and
[tex]f(-6)=2(-6)+7=-12+7=-5[/tex]Therefore, f(3)=13 and f(-6)=-5.