To calculate the height of a ball thrown upward at 64 ft/sec from an initial height of 80 ft, one must derive the position function using the equations of motion under constant gravity. The process involves integrating the vertical acceleration, a(t), to find the vertical velocity, v(t), and then integrating v(t) to obtain the vertical displacement, z(t). The equations are v(t) = gt + v_0 and z(t) = (1/2)gt^2 + v_0t + z_0, where g represents gravitational acceleration. Initial conditions, such as initial velocity and height, are used to determine the constants v0 and z0. This method provides a comprehensive way to model projectile motion in a gravitational field.