Lenna knows how to play tennis but wants to learn badminton. positive transfer learning is most likely to occur when she: confuses her knowledge and skills in tennis with the rules and shots used in badminton

The answer is "when she uses her knowledge and skills in tennis to understand the rules and shots used in badminton".

Transfer of learning is so basic in our regular daily existences that we may not understand that we are applying exchange to our ordinary practices. We do this without cognizant idea. Exchange can be viewed as positive or negative. 
Positive Transfer refers to a transfer of learning to be sure when the learning or preparing did in one circumstance demonstrates supportive to learning in another circumstance.