To do it without subbing in numbers (ie if this was a 'fill in the blank' question) you would need the midpoint of that segment. That's just [ (x1+x2)/2 , (y1+y2)/2 ] = (5, 3).
With a slope of -2 you get y-3 = -2(x-5) which simplifies to y = -2x +13 which is y + 2x = 13, choice A.