Out of 100 students surveyed: 54 students have a brother. 42 students have a sister. 18 students have neither a brother nor a sister. What is the probability of a randomly chosen student having a brother given that he already has a sister?

• A$\frac{3}{3}$
• B$\frac{16}{3}$
• C$\frac{16}{15}$
• D$\frac{1}{3}$

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