Answer
a) $-\dfrac{1}{3}$
b) When $x$ decreases by $3$ units, $y$ increases by $1$ unit.
Work Step by Step
We know that by the Slope Formula: if $P_1(x_1,y_1)$ and $P_2(x_2,y_2)$ are on a line, then the slope is: $m=\dfrac{y_2-y_1}{x_2-x_1}$.
a) SOlve for the slope using the formula above to obtain $m=\dfrac{2-1}{-2-1}=-\dfrac{1}{3}$.
b) A slope of $-\dfrac{1}{3}$ means that if $x$ decreases by $3$ units, then $y$ increases by $1$ unit.
