Two friends are practising their tennis serve. Adam can serve 6 balls per minute while Mark can
serve 4 balls per minute. Adam brings a bag of balls which he serves at Mark. Once Mark has 18
balls on his side of the court he begins serving. Adam continues to serve until his bag is empty
and then must wait 11 minutes for Mark to return all the balls.
Assuming no additional time is spent gathering balls, how many balls were in Adam's bag?
A 44
B 45
C 62
UCLES 2018
9694/13/O/N/18