Find the value of y so that line is passing through two points

Slope of a line passing through two given points 
= (y2-y1)/(x2-x1)

For m=3, and substituting coordinates,
3=(1-y)/(4-1)
solve for  y
1-y=3*3=9
y=1-9=-8

y=-8

Idon’t see a picture