I am confused on (b) I'm used to plugging in a function, just using the graph, I can see f(-4) is 4 ..... but then the h is still in the denominator? am I overthinking it? This is the whole question on the assignment page

Exercises: #4 96 4. Use the following graph of the function f to answer the questions below. .10 10 FIGURE 1. Graph of f() (a) s'(0) = 0 (b) lima-+o f(-4+h)-1(4 =