slope intercept form follows this general equation...
\(y=mx+b\)
With this information you have posted, all you can do is find slope, your m. To calculate for slope, you need to use this following equation...
\(m= \frac{y_2-y_1}{x_2-x_1}\)
Then, you pick one of your coordinate pairs to be 1 and the other to be 2. I will choose the first coordinate pair as 1, so...
\(m=\frac{-1-3}{7-3} =-1\)
You plug in -1 into your slope formula...
\(y=-1x+b\)
Now, to find your y-intercept, or b, you must plug in one of your coordinate pairs. In that equation, you may plug in the values (3,3), so you'll have...
\(3=-1(3)+b\)
Just solve for b and you will be done