If ∠ BOE = 40 then ∠ BOD = 80 then ∠ AOC = 80 then ∠ COF = 90-80 = 10.

If ∠ BOE = x (x < 45), ∠ BOD = 2x, ∠ AOC = 2x, ∠ COF = 90-2x.