Question 1123163
draw this
h=-9.8t^2+18t+36
want h=4
therefore 
-9.8t^2+18t+32=0
t=(-1/19.6)-18+/-sqrt(324+1254.4); sqrt term is equal to 39.73, use negative root only
t=(-1/19.6)(-57.73)=2.95 seconds
{{{graph(300,300,-10,10,-50,60,-9.8x^2+18x+36,4)}}}