21) An object in launched upward at 64 feet per second (ft/s) from a platform 80 feet high. The equation for the object's height in $\mathrm{ft}$ based on time in seconds is given by $h=-16 x^{2}+64 x+80$

Step 1 ：Given the equation for the object's height: \(h = -16x^2 + 64x + 80\)

Step 2 ：Identify the coefficients: \(a = -16\), \(b = 64\), and \(c = 80\)

Step 3 ：Find the vertex of the parabola: \(h = -16(x - h)^2 + k\)

Step 4 ：Calculate the x-coordinate of the vertex: \(h = \frac{-b}{2a} = \frac{-64}{2(-16)} = 2.0\)

Step 5 ：Calculate the y-coordinate of the vertex: \(k = -16(2 - 2)^2 + 64(2) + 80 = 144.0\)

Step 6 ：\(\boxed{\text{The maximum height the object reaches is 144 feet, and it takes 2 seconds to reach that height.}}\)