First, you can plug this into the point slope formula. you will have to do that before you can get the slope intercept form. Plug in what you know. m is slope, so plug in -1/3 for m. The point given can be plugged in to the formula also. This is what it should look like:
y + 7 = -1/3(x + 3)
***** Note that the -3 and -7 become positive because it is subtracting negative numbers and 2 negatives make a positive. *************************