Question 1181972
h(t)=-16t^2+34t+15
set it equal to 0, the ground.
may rewrite as 
16t^2-34t-15=0, multiplying by -1
t=(1/32)(34+/-sqrt(2116))
=(1/32)(80), only positive root of 2.5 seconds.

{{{graph(300,300,-5,5,-10,35,-16x^2+34x+15)}}}