The unit vector which is orthogonal to the vector 3i + 2j + 6k and is coplanar with the vectors 2i + j + k and i - j + k is
a. 2i - 6j + k/√41
b. 3j - k/√10
c. 2i - 3j/√13
d. 4i +3j - 3k/√34