I hope this helps you
f (1+1)= f (1)+8
f (2)= 27+8
f (2)=35
f (2+1)= f (2)+8
f (3)= 35+8
f (3)=43
Step-by-step explanation:

5x+9 = 10x-9
Take 5x from both sides
9 = 5x-9
Add 9 to both sides
18 = 5x
Divide by 5
3.6=x
Kx-3y=k
y=4x+1 ( we will put it in 1st equation )
kx - 3 (4x+1)=k
kx - 12 x - 3 =k
kx - 12 x = k+3
x(k-12) = k+3
x=

Also y=

We can not divide with zero.
k-12=0
k=12For k= 12 equations have no solutions.