A projectile is launched from ground level with an initial velocity of v 0 feet per second. Neglecting air resistance, its height in feet t seconds after launch is given by s= -16t^2 + v 0 t. Find the time(s) that the projectile will (a) reach a height of 80 ft and (b) return to the ground when v0 = 112 feet per second. (a) Find the time(s) that the projectile will reach a height of 86 ft when v 0= 112 feet per second. Select the correct choice below and, if necessary, fill in the answer box to complete your choice.