Answer: 3000
Ask yourself this: "Is 3148 closer to 3000, or is it closer to 4000?"
The answer is 3000 since 3148-3000 = 148 while 4000-3148 = 852
Put another way, we round 3148 to 3000 since the next digit after the thousands place is not a 5 or larger. So we just drop the 148 and replace those digits with 0s.