If a^2+b^2+49 c^2+18=2(b-28 c-a) then the value of (a+b-7 c) is:

If $a^2 +b^2 +49c^2 + 18 = 2(b - 28c - a)$

then the value of (a - b - 7c) = ?

we can find the values of the variables by =

Coefficient of variables on right sides divide by coefficient of same variable on left side along with the signs as given below = 

b = 1

a = -1

c = -\(\frac{28}{49}\) = -\(\frac{4}{7}\)

(a + b - 7c) = (-1 + 1 - 7(-\(\frac{4}{7}\))) = 4