Subject: mathqa
Question: at 15 : 00 there were 20 students in the computer lab . at 15 : 03 and every three minutes after that , 3 students entered the lab . if at 15 : 10 and every ten minutes after that 9 students left the lab , how many students were in the computer lab at 15 : 44 ?
Option: 
A: 7
B: 14
C: 30
D: 25
Answer: D