Find the Average Rate of Change Illustrated in the Graph $\mathrm { f } ( \mathrm { x } ) = 3.1 \mathrm { x } + 33$

Find the average rate of change illustrated in the graph.
-The linear function $\mathrm { f } ( \mathrm { x } ) = 3.1 \mathrm { x } + 33$ models the percentage of people, $\mathrm { f } ( \mathrm { x } )$ , who graduated from college $x$ years after 1998. Find and interpret the slope.

A) $\mathrm { m } = 3.1$ ; the percentage of people graduating from college has decreased at a rate of $3.1 \%$ per year since $1998 .$

B) $\mathrm { m } = 33$ ; the percentage of people graduating from college has increased at a rate of $33 \%$ per year since $1998 .$
C) $\mathrm { m } = - 3.1$ ; the percentage of people graduating from college has decreased at a rate of $3.1 \%$ per year since $1998 .$

D) $m = 3.1$ ; the percentage of people graduating from college has increased at a rate of $3.1 \%$ per year since $1998 .$