If bc + cd = 2bd and a + c = 2b, then which one of the following is correct?

If (3a +6b +c +2d) x (3a - 6b - c +2d) = (3a - 6b +c- 2d) x (3a +6b - c- 2d), then which one of the following is correct ?

If a, b, c, d, e and f satisfy 2a = 3b = 6c = 9d = 12e = 18f, then what is the value of (a + b)/(c + d + e + f)?

If x + (1/y) = 1 and y + (1/z) = 1, then the value of z + (1/x) is

If a^b = c^d, then log a / log c is

If x^3 – y^3 = 117/8 and x – y = 3/2 then the value of x^2 + xy + y^2 will be