Aball was thrown upward into the air. the height, in feet, of the ball above the ground t seconds after being thrown can be determined by the expression -16t^2 + 40t +3. what is the meaning of the 3 in the expression?

The 3 has no relation to time. Therefore, it is the starting position of the ball. Since the expression is the height, in feet, of the ball above the ground, the 3 means that the ball started 3 feet above ground when thrown.

For future knowledge, the t^2 means that -16 is the initial acceleration of the ball, and the t means that 40 is initial velocity.