Question 798319
If x is time and y is height above ground, 
then directly using y=10, simplifying and using solution to quadratic equation, 
x=12.6 or x=45.  I omit showing those steps.  


The parabola has  a maximum and opens downward.  


You can complete the square to convert y into standard form.


If rendering works correctly, the graph should appear like,

{{{graph(300,300,-10,65,-10,30,-0.017x^2 + 0.98x + 0.33)}}}



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Generally, {{{y=ax^2+bx+c}}}
For {{{y=0}}}, {{{x=(-b+- sqrt(b^2-4ac))/(2a)}}}


Tell me if you need to see more steps.