Answer
$a). v=2gt,h=gt^{2}$
$b).$ total maximum height$=3gt^{2}$
$c).$ Maximum height $=26460m$
Work Step by Step
a) a=2g,
$v=0+at=2gt$
$h=0+\frac{1}{2}2g\times t^{2}=gt^{2}$
b). $v^{2}=u^{2}+2aS$
$0=(2gt)^{2}-2gS$
$S=2gt^{2}$
So, total maximum height$=2gt^{2}+gt^{2}=3gt^{2}$
c). t=30s,
Maximum height $=3\times 9.8 \times 900=26460m$