The real answer is going to be 23.5
You can download the answer here
bit.ly/3a8Nt8n
It is the line of symmetry of a parabola and divides a parabola into two equal halves that are reflections of each other about the line of symmetry.
It intersects a parabola at its vertex.
It is a vertical line with the equation of x = -b/2a.
Easy peasy
the average rate of change in section A is the slope from (1,g(1)) to (2,g(2))
the average rate of chagne in section B is the slope from (3,g(3)) to (4,g(4))
A.
section A
g(1)=4(3)^1=12
g(2)=4(3)^2=4(9)=36
slope=(36-12)/(2-1)=24/1=24
section B
g(3)=4(3)^3=4(27)=108
g(4)=4(3)^4=4(81)=324
slope=(324-108)/(4-3)=216/1=216
section A has an average rate of change of 24
section B has an average rate of change of 216
Here is a proportion
5/2 = x/8
2x = 40
/2 /2
x = 20
Hope this helps