The sum of all angles in an octagon is given by
180*(n-2) >>>>>>>>>with n = 8
180*(8-2) = 1080 degrees
A + B = 1080 .......where
A is the angle of an octagon which is twice that of the other seven angles
B equals the sum of the other seven angles
If we assume each angle of B is equal to each other, then
B = x+x+x+x+x+x+x = 7x
And A = 2x
The equation that results is
A + B = 2x +7x = 9x =1080
x = 120 degrees
2x = A = 240 degrees