For What Value(s)of a Is the Vector $\vec { v } = 3 \vec { i } + a \vec { j } + 3 \vec { k }$

Essay

For what value(s)of a is the vector $\vec { v } = 3 \vec { i } + a \vec { j } + 3 \vec { k }$ parallel to the plane $z = 2 x - 5 y + 2$ ?