Let A,B,C be three equally likely and collectively exhaustive events. If the odds 8 : 3 against A, 5:2 against B then the odds against C are

Question

$\begin {array} {1 1} (A)\;20:17 & \quad (B)\;50:31 \\ (C)\;3:34 & \quad (D)\;77:34 \end {array}$