Solution :
We know,

Net debt = debt market value - excess cash
= 110 - 10
= 100 million dollar


= 0.25


= 0.75
Therefore, WACC = 0.75 x 12% + 0.25 x 5% x (1 - 31%)
= 0.75 x 12% + 0.25 x 5% x (1 - 0.31)
= 0.75 x 12% + 0.25 x 5% x 0.69
= 9% + 0.862%
= 9.862%