Vector Algebra

a and b are two vectors such that a is not parallel to b. If $\mathbf{p}=(x+2 y+3) \mathbf{a}+(5 x-y+2) \mathbf{b}$ and $\mathbf{q}=(2 x+3 y+5) \mathbf{a}+(x-5 y-2) \mathbf{b}$ are two vectors such that $\mathbf{p}=2 \mathbf{q}$, then $x-2 y=$