4. Mia is helping her mother pick up 30 toys from the floor. Her mother puts three toys into the storage box every 30 seconds, while at the same time, Mia throws out two toys that were put into the box in the previous 30 seconds. After ( ) minutes, Mia and her mother first manage to put all the toys into the storage box.
(A) 13.5
(B) 14
(C) 14.5
(D) 15.5
(E) 15
4. B.
$$
(30+(30-3) \div(3-2) \times 30) \div 60=14 \text {. }
$$