Which equation represents the line that passes through points -3,7 and 9,1

To solve this type of problem, you need to first find the slope of the final equation, which can be found with a set of two points, and the formula for that is:  
 
Now, plug in the values from your two points:  
 
Your slope is -2. From here, you need to plug it into point-slope form.  
 
and  correspond to one of the points you specified. It doesn't matter which one. Regular y and x are just variables, and m is the slope. I chose the first point. Plug everything in:  
 
 
 
Your final answer is y = -2x + 1