This is true, but it may work better to think about what it means, rather than memorizing an equation.

If h=1, you want a point where the x is 1 more than the point you're starting with. (If h=2, you want a point where the x is 2 more, etc.)

The point you're starting with has , so you want a point where .

Then go back to your equation and plug in x=3:

So your point is (3,9).

Then just find an equation of the line passing through (2,4) and (3,9).