Chapter 11 - Section 11.2 - Solving Quadratic Equations by Completing the Square - Exercise Set - Page 778: 65

2.8 seconds

$h=-16t^2-20t+180$ $0=-16t^2-20t+180$ $0/-4=(-16t^2-20t+180)/-4$ $0=4t^2+5-45$ $x=(-b±\sqrt {b^2-4ac})/2a$ $x=(-5±\sqrt {5^2-4*4*-45})/2*4$ $x=(-5±\sqrt {25+720})/8$ $x=(-5±\sqrt {745})/8$ We are dealing with time, so we want only the positive square root. $x=(-5±\sqrt {745})/8$ $x=(-5+\sqrt {745})/8$ $x=(-5+27.29)/8$ $x=22.29/8$ $x=2.786$