Answer:
24
Step-by-step explanation:
f(n) = f(n − 1) + 3
if n = 7 => f(7) = f(7-1) + 3 = f(6) + 3
if n = 6 => f(6) = f(6-1) + 3 = f(5) + 3
if n = 5 => f(5) = f(5-1) + 3 = f(4) + 3
if n = 4 => f(4) = f(4-1) + 3 = f(3) + 3
if n = 3 => f(3) = f(3-1) + 3 = f(2) + 3
if n = 2 => f(2) = f(2-1) + 3 = f(1) + 3
if f(1) = 6 then f(2) = 9
f(3) = 12
f(4) = 15
f(5) = 18
f(6) = 21
f(7) = 24
Answer:

Step-by-step explanation:
Given
The attached graph
Required
Determine the range of the graph
First, we list out the coordinate of each point on the graph:
The points are:

A function has the form: (x,y)
Where
y = range:
From the coordinate points above,

Order from least to greatest"

Hence, the range are: 
1. Solve the bracket 4×x and 4 × -7
4x-28=2x-6
2. Get the x on one side and the numbers on the other so: first +28
4x=2x+22 now -2x
so 2x=22 and now you only need to divide into 2
x=11