First you need to find the slope using y2-y1/x2-x1, which is 7-3/31 you'll get 2 and thats the slope (m).
Next, use the formula: y - y1 = m (x - x1)
Plug in ONE of the points just ONE instead of x1 and y1, (Either one of them it doesnt matter) which is: (using the first point) y - 3 = 2(x - 1) after solving you'll get: y = 2x + 1 which is the answer
Hope this helped!