Kenny you are so close with the correct formula equation. In fact trigonometry will give you the answer, but you're just a pinch off with your thoughts. Trig'n it will work, but we need to know how far away, horizontally speaking
with a 90 degree angle of measurement, the tide is so we can determine vertical height increase, (or decrease), the ground we stand on is different from one another. This height variation will tell us if we need to add or subtract when we get
further into our equation. Then there comes in the max high and max low tide level-the difference, which such would need to be multiplied by the tangent of, and then added to the height variation of 90 degree angle. It's actually way
more simple to do in person than explain.