I will assume we are talking about baskets that are only half full. As opposed to 3 AND 1/2 baskets.
total=amount picked by boys + amount picked by girls
total=3(1/2)+5(1/2)
total=4 baskets <---Answer
if you did mean 3 AND 1/2 baskets then the answer is the following:
total=amount picked by boys+amount picked by girls
= 3+1/2 + 5+1/2
=9 baskets <---Answer