For example, consider the simple number line:
| - | - | - |
1 - | - | - 4
Here, we travel 3 ticks from 1 to arrive at 4, so travelling three ticks increases our value by 3, so therefore travelling one tick increases our value by 1 (3/3 = 1)
Going back the number line in your question, we don't know exactly how much we add on with each tick travelled, but we do know that travelling 5 ticks from 2 adds on 40, since 2 + 40 = 42.
From this can you work out how much we add on when we travel one tick? When you have that value, you should be able to work out x, by travelling two ticks from 2.
Hope this helps.