All we have to pay attention to in this problem is B, so we can ignore the rest of the triangle. B is 5 units directly to the left of line <em>l</em>, meaning that B' must be 5 units to the right of line <em>l.</em> This would put B' 2 units to the left of line <em>m.</em> That means that B" would be 2 unit to the right of line <em>m</em>, as that is how reflections work. Adding up all of the difference in units you have a 10 unit shift from B to B', and then a 4 unit shift from B' to B". Now adding 4+10=14 units.
