Question 1206244
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The basic definition of probability is this:

               # of ways event can happen
  P(event) = ------------------------------
              total # of possible outcomes

By definition, P(B|A) is the probability that B happens, given that A happens.

With that definition, the denominator of the probability fraction is the probability that A happens, because the only part of the sample space you are concerned with is the outcomes in which A happens.  And the numerator is the probability that both A and B happen:

            P(A ∩ B)
  P(B|A) = ----------
              P(A)

In your problem, the given information is the numerator and denominator of this fraction, so

            .06
  P(B|A) = ----- = 0.2
            0.3</pre>