This is the concept of application of quadratic expressions. Given that the height of the ball is modeled by the equation; h=-7.3t^2+8.25t+2.1+5 The time taken for the ball to hit the ground will be given as falls; -7.3t^2+8.25t+7.1=0 to solve for t we use the quadratic formula; t=[-b+/-sqrt(b^2-4ac)]/(2a) a=-7.3, b=8.25, c=2.1 t=[-8.25+/-sqrt[8.25^2+4*7.3*7.1]/(-2*7.3) t= -0.572 or t=1.702 since there is not negative time we take the time taken for the ball to hit the ground will be: t=1.702 sec