Need help I don’t understand what it means

Answer:
b) - 10
Step-by-step explanation:
To find the average rate of change, we have divide the change in y of f(x) , by the change in x(input).
[tex]\sf \boxed{\text{\bf Average rate of change = $\dfrac{f(b)-f(a)}{b-a}$}}[/tex]
a = 4 ; f(a) = -17
b = 6 ; f(b) = -37
[tex]\sf Average \ rate \ of \ change = \dfrac{-37-[-17]}{6-4}[/tex]
[tex]\sf =\dfrac{-37+17}{2}\\\\=\dfrac{-20}{2}\\\\=-10[/tex]