This type of problem is an exercise in substituting a value (such as 9) for a variable (such as x).

1. Find: G(9) if G(x) = 2x + 3

we replace x with 9 in the above equation so:

G(9) = 2*9+3 .........|replace x with 9

G(9) = 18+3 ...........|multiplacation before addition (PEMDAS)

G(9) = 21

Try to do the second one here as a reply and I will correct you.