Find the Average Rate of Change Illustrated in the Graph $f ( x ) = 1.8 x + 22$

Find the average rate of change illustrated in the graph.
-The linear function $f ( x ) = 1.8 x + 22$ models the percentage of people, $f ( x )$ , who graduated from college $x$ years after 1998. Find and interpret the slope.

A) $\mathrm { m } = 1.8$ ; the percentage of people graduating from college has decreased at a rate of $1.8 \%$ per year since 1998 .
B) $\mathrm { m } = 22$ ; the percentage of people graduating from college has increased at a rate of $22 \%$ per year since 1998 .
C) $\mathrm { m } = 1.8$ ; the percentage of people graduating from college has increased at a rate of $1.8 \%$ per year since 1998 .
D) $m = - 1.8$ ; the percentage of people graduating from college has decreased at a rate of $1.8 \%$ per year since 1998 .