If $9a^2 + 4b^2 + 49c^2 + 18 = 2(2b + 28c - 3a)$, then the value of (a + 2b - c) will be :

$\frac{11}{21}$ $\frac{2}{21}$ $\frac{26}{21}$ $\frac{5}{21}$

$\frac{2}{21}$