Point b is on a line with a slope of 3. which choice could be the coordinates of another point on this line?

You can find the appropriate selection by plotting the points on the graph (actually, or mentally) and seeing which is on the line that goes 3 units up for every 1 unit to the right.

We see the point (1, 1) differs from point B in x-value by -1 and in y-value by -3, so it will be on the line with slope -3/-1 = 3 through point B.

The appropriate choice is
  (1, 1)