20. if a certain linear function f(x) is evaluated at 0, the answer is 4.
in other words, f(0) = 4. if the same function f(x) is evaluated
at 3, the answer is 5. in other words, f(3) =5. use this
information to find the equation of the function in f(x)= mx + b
form.

y = (1/3)x + 4

Step-by-step explanation:

Two points on this line are (0, 4) and (3, 5).

As we move from the first point to the second, x increases by 3 and y increases by 1.  Thus, the slope, m, of the line is m = rise / run = 1/3.

Use the slope-intercept equation:  y = mx + b.

If we use the data from the point (0, 4), we get:

4 = (1/3)(0) + b, so that b = 4.  The desired equation is y = (1/3)x + 4.