I to solve a problem, I solved 2 out of 3 questions now I'm stuck. Sorry if it's not well written, I translated from french.

During a basketball game, Mary throws the ball in the basket. The trajectory of the ball can be represented by the equationh = -0,078d^2 + 0,92d + 2question: What is the maximum height the ball can reach

I've tried finding the vortex because that seems to make sense in this context but it gives me an answer like -0,78m. This doesn't make sense because it's negative and in the previous question I found that the initial height of the ball is 2m, the maximum height can't be lower than the initial height.

thanks