Probability Word Problem?

The answers listed do not cover the case where Keiko gets zero heads (and if Ephraim also flipped tails|tails the joint probability would be 1/8) so I'll assume the answers listed apply to Keiko flipping 1 head. This would mean that Keiko flips a head (1/2) and Ephraim flips a head and a tail so we count the cases for head|tail and tail|head (1/4 +1/4) giving a joint probability of (1/2)*(1/2) = 1/4. So A.