Can someone please help me with this,

so far i have

$\displaystyle x_{P} = 0 $

$\displaystyle Z_{P} = ct^{\beta}$

$\displaystyle x_{m} = l sin\theta $

$\displaystyle Z_{m} = lcos\theta $

However when I do the time derivatives I dont get the above answer. so my coordinates must be wrong? Can anyone suggest an alternative or see where I have gone wrong.