First, find the slope of the line between the two points using

Then use one point to calculate the b for
.
Step 1: slope
![\begin{aligned}m&=\dfrac{7-4}{-4-2}\\[0.5em]&=\dfrac{3}{-6}\\[0.5em]&=-\dfrac{1}{2}\end{aligned}](https://tex.z-dn.net/?f=%5Cbegin%7Baligned%7Dm%26%3D%5Cdfrac%7B7-4%7D%7B-4-2%7D%5C%5C%5B0.5em%5D%26%3D%5Cdfrac%7B3%7D%7B-6%7D%5C%5C%5B0.5em%5D%26%3D-%5Cdfrac%7B1%7D%7B2%7D%5Cend%7Baligned%7D)
Step 2: calculate b
Right now we have
, so we'll plug in (2,4) for the x and y:
![\begin{aligned}\\4&=-\frac{1}{2}(2)+b\\[0.5em]4&=-1+b\\[0.5em]5&=b\end{aligned}](https://tex.z-dn.net/?f=%5Cbegin%7Baligned%7D%5C%5C4%26%3D-%5Cfrac%7B1%7D%7B2%7D%282%29%2Bb%5C%5C%5B0.5em%5D4%26%3D-1%2Bb%5C%5C%5B0.5em%5D5%26%3Db%5Cend%7Baligned%7D)
Now we build our slope-intercept equation: 
But, this isn't standard form. We need to clear out the fraction and then move the x-term to the left.
Can you take it from there?