By using the suvat equations:
(a) \(v^2=u^2+2as\) for the vertical components, so
\(0^2=(5sin57)^2+2*-9.81*s\)
therefore s=0.896m
However, since the ramp is 1.2m above the ground, the skateboarder is 0.896+1.2=2.096m above the ground.
(b) Work out the time when the skateboarder reaches the highest point
v=u+at for the vertical components, so 0=5sin57-9.81t, therefore t=0.427s
Now using the horizontal components: s=ut, so s=5cos570.427=1.164m