Y= x³ + (x+2)³ + (x+4)³ over 24, y = 3x + 6 now set one equation in the system equal to f(x) and the other equal to g(x). graph f(x) and g(x).

We have that
Y = [x³ + (x+2)³ + (x+4)³]/24
 y = 3x + 6

f(x)=[x³ + (x+2)³ + (x+4)³]/24
g(x)=3x + 6

using a graph tool
see the attached figure

the solution of the system are
x1=-6
x2=-2
x3=2

the solution are the points
(-6,-12)
(-2,0)
(2,12)

Y= -2x-1 the negative in front of the 2 is because the slope is negative and the -1 is because it’s down 1 on the y axis.