mgh=3*1/2mv^2
mgh+1/2mv^2=1/2mV0^2
mgh+1/3mgh=1/2mv0^2
4/3mgh=1/2mv0^2
h=3/8v0^2/g=3/8*40^2/10=60m
60=40t-1/2gt^2
120=80t-gt^2
12=8t-t^2
t^2-8t+12=0
t=2s,t=6s