Answer:
f(x) = 6x -26
Explanation:
You want a linear function f with the values f(5) = 4 and f(3) = -8.
Constant slope
One way to do this is to make use of the fact that the ratio of rise to run is the same for all point pairs on the line:
(y -y1)/(x -x1) = (y2 -y1)/(x2 -x1)
(y -4)/(x -5) = (-8 -4)/(3 -5) . . . . . . . . . fill in given point values
-2(y -4) = -12(x -5) . . . . . . . . . . . . cross multiply
y -4 = 6(x -5) . . . . . . . . divide by -2
f(x) = 6x -26 . . . . . . add 4 and simplify; desired functional form