Line MN passes through points M(4, 3) and N(7, 12). If the equation of the line is written in slope-intercept form, y = mx + b, what is the value of b?

–15
–9
3
9

Question

Line MN passes through points M(4, 3) and N(7, 12). If the equation of the line is written in slope-intercept form, y = mx + b, what is the value of b?

–15
–9
3
9

supie · Answer

Ok so what we have to do is find the slope. 
$$(12 - 3) / (7 - 4) = 9 / 3 = 3$$
$$3=3\ is\ true\ so\ m=3$$ and $$y = 3x + b$$ but when $$y = 3$$$$x = 4$$ So we plug in the numbers from the variables
$$3 = 3 (4) + b$$$$b + 12 = 3$$
$$\ b\ =\ ?$$