If an object is propelled upward from a height of h feet at an initial velocity of v feet per second, then its height after t seconds is given by the equation S= - 1612 + vt + h, where S is in feet. If the object is propelled from a height of 12 feet with an initial velocity of 64 feet per second, its height S is given by the equation
S= - 162 +64 +12.
After how many seconds is the height 40 feet?