7x - y - 6 = 0
x - 2y + 1 = 0
3x - 2y - 1 = 0
x - 7y + 6 = 0
The respective values of \( |\vec{a}| \) and} \( |\vec{b}| \), if given \[ (\vec{a} - \vec{b}) \cdot (\vec{a} + \vec{b}) = 512 \quad \text{and} \quad |\vec{a}| = 3 |\vec{b}|, \] are: