Explanation:
the slow intercept form is
y = ax + b
the slope is always the factor a of x (in every line equation).
it is defined as the ratio y/x expressing how many units y changes, when x changes a certain amount of units - e.g. when going from one point on the line to another.
so, for the given 2 points x changes by -5 (from 7 to 2), and y changes by +10 (from 2 to 12).
therefore, the slope is 10/-5 = -2
our line equation looks more like
y = -2x + b
to get b we use the coordinates of one of the points.
e.g. 7, 2
2 = -2×7 + b = -14 + b
b = 16
or full line equation is
y = -2x + 16