h=1/2gt^2
h-25=1/2g(t-2)^2=1/2gt^2-25
g(t-2)^2=gt^2-50
50=g(t^2-(t-2)^2)=g(t^2-t^2+2t-4)
2t-4=5
2t=9
t=4.5s
h=1/2gt^2=1/2*10*4.5^2=101.25m