$f(−1) = 7$ represents the point $(−1,7)$.
Graph this point and the point corresponding to $f(3) = 8$ in order to sketch the line.

Use the $y = mx + b$ format wherem = slope (growth) and $b=y$-intercept (starting point).

Find the growth and substitute one of the coordinates of a point in the problem and solve for b.

A line $g(x)$ that is perpendicular to $f(x)$ has a slope that is the negative reciprocal of the slope of the line $f(x)$.