Which of the following is the correct formal definition of the conditional probability P(B|A)?

Algebraically derive Bayes' theorem starting from the conditional probability identity $P\left(B\mid A\right)=P(A\cap B)/P\left(A\right)$ and $P\left(A\mid B\right)=P(A\cap B)/P\left(B\right)$. Which equation correctly shows the derivation of Bayes' formula?

Two boxes are used: Box 1 contains 3 red and 2 blue marbles, Box 2 contains 1 red and 4 blue marbles. A box is chosen with probabilities 0.6 for Box 1 and 0.4 for Box 2. A marble drawn is red. What is the probability it came from Box 1?

A survey of drivers recorded whether each driver texted while driving and whether they received a warning last year. The counts from the survey show that $30$ drivers both texted while driving and received a warning, and $120$ drivers received a warning in total. What is the probability that a driver texts while driving, given that they received a warning last year?