Need help solving this problem. Code keeps being incorrect.

$3\mathrm{.}2[4$ pt$]$ Given the vectors, $u=[2,-10,4],v=[3,4,15],$ and $w=[-2,1,x],$ find the value of $x$ such that they are linearly dependent. If instead, the vectors were $u=[2,z,4],v=[3,4,15],$ and $w=[-2,1,2],$ find the value of $z$ such they are linearly dependent. Store the values of $x$ and $z$ in the variables $x$ and $z.$