one way is subsitution, but that's no fun
use
y-y1=m(x-x1)
a point is (x1,y1)) and the slope is m
so slope between the oints (-2,1) and (1,10) is
(10-1)/(1-(-2))=9/(1+2)=9/3=3
a point is (1,10)
y-10=3(x-1)
exapand
y-10=3x-3
solve for constant
minus 3 both sides and add 10
y-3x=7
times -1
3x-y=-7
A is answer
