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The quadratic formula has nothing to do with this problem.
It is about finding the maximum of a quadratic function.
Solution
The maximum is where the VERTEX is.
The x-coordinate of the vertex is at x = , where "a" is the coefficient at x^2 and "b" is the coefficient at x.
In your case, a = -0.02, b = 1.0, so the x-coordinate of the vertex is
x = = = 25.
Thus we just found the horizontal coordinate: the maximum will happen at x = 25 feet.
Now, to find the maximum height (y-coordinate), substitute x= 25 into the given formula for the height.
That's all.
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On finding the maximum/minimum of a quadratic function see the lessons
- HOW TO complete the square to find the minimum/maximum of a quadratic function
- Briefly on finding the minimum/maximum of a quadratic function
- HOW TO complete the square to find the vertex of a parabola
- Briefly on finding the vertex of a parabola
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this textbook under the topic "Finding minimum/maximum of quadratic functions".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson
to your archive and use it when it is needed.
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Post-solution note
Wording in your problem is terrible ---- TOOOOOOOO many EXCESSIVE UNNECESSARY words.