A slingshot, which can be modeled as a spring with spring constant k = 81.9 N/m, is stretched by 22 cm with respect to its equilibrium position and used to shoot a rock with mass 0.09 kg straight up...

Extracted text: A slingshot, which can be modeled as a spring with spring constant k = 81.9 N/m, is stretched by 22 cm with respect to its equilibrium position and used to shoot a rock with mass 0.09 kg straight up into the air. Find the speed of the rock (in m/s) when it reaches a height which is 25% of its maximum height (relative to the position at which it was shot from). Use g = 9.81 m/s?. Hint: First find the maximum height, and then find the speed when the height is 25% of that.