The ball hits the ground when h=0, 5(5-t-t²)=0.
t²+t-5=0. t²+t=5, t²+t+¼=5¼, (t+½)²=5¼.
t+½=±√(21/4)=±√21/2=±4.5826/2=±2.2913.
So t=-0.5 ±2.2913. We reject the negative solution because t starts from zero so negative values are out of range. Therefore t=1.79 seconds.
