Let:
A = students who passed the test = 14
B = students who completed the assignment = 13
N = Total students = 22
(A⁺ ∩ B⁺) = 6
P(A ∪ B) = 1 - 6/22 = 8/11
P(A ∩ B) = P(A) + P(B) - P(A ∪ B) = 14/22 + 13/22 - 8/11 = 1/2
P(A|B) = P(A ∩ B)/P(B) = (1/2)/(13/22) = 11/13 ≈ 0.85 ≈ 85%