[tex] P(B|A)=\dfrac{P(A \cap B)}{P(A)}\\\\
|\Omega|=15\cdot14=210\\
|A|=3\cdot14=42\\
|A \cap B|=3\cdot7=21\\\\
P(A)=\dfrac{42}{210}=\dfrac{7}{35}\\
P(A \cap B)=\dfrac{21}{210}=\dfrac{1}{10}\\\\
P(B|A)=\dfrac{\dfrac{1}{10}}{\dfrac{7}{35}}=\dfrac{1}{10}\cdot\dfrac{35}{7}=\dfrac{1}{2}\Rightarrow \text{D} [/tex]
