What is the equation of the line passing through the points (3,9) and (-1,-15)

(x+2)+(x+2)+(x+4)+(x+4)

Something to keep in mind, these are all being added together. N0 multiplication is needed. 

x+x+x+x= 4x

2+2+4+4=12

But, there is nothing equal to 4x+12, so we can use the distributive property to find something equivalent. 

4*x=4x 4*3=12

So, 4(x+3) "C" < the answer

I hope this helps!
~kaikers