Suppose s and t are mutually exclusive events. find p(s or t)? sp(s) = 6/11 and p(t)= 1/10

Using P(A∪B) = P(A) + P (B) - P(A∩B) 
If we apply this in the question 
Then P(S∪T) = P(S) + P(T) - P (S∩T)
                      = 6/11 + 1/10 - P (S∩T)
                      = 71/110 - P (S∩T)
But events S and T are mutually exclusive events therefore, 
P(S∩T) = 0,
Hence P(S∪T) = 71/110