Explanation:
For 6+7, on a number line we have placed a point A on value 6. On moving 7 units in the rightwards direction a point B is marked. That means when we move from 0 to point B, we get the result for 6+7 = 13.
For 8+4, on a number line we have placed a point C on value 8. On moving 4 units in the rightwards direction a point D is marked. That means when we move from 0 to point D, we get the result for 8+4 = 12.
For 2+9, on a number line we have placed a point E on value 2. On moving 9 units in the rightwards direction a point F is marked. That means when we move from 0 to point F, we get the result for 2+9 = 11.