Answer:
step 1. h(t) = -16t^2 + 48t + 288. Set this equal to 320.
step 2. -16t^2 +48t + 288 = 320
step 3. -16t^2 + 48t - 32 = 0
step 4. -16(t^2 - 3t + 2)
step 5. -16(t - 2)(t - 1)
step 6. The ball reaches 320 feet "both!!!" at t = 1, 2 seconds once going up and once coming down.