The question asks: if we already know that event E has happened, what is the probability that event F also happens? This is what conditional probability means.
The formula for conditional probability of F given E is:
P(F∣E)=P(E)P(E∩F)
P(E)=31
P(F)=41
P(E∩F)=51
Plugging into the formula:
P(F∣E)=P(E)P(E∩F)
P(F∣E)=3151=51×13=53