In a coin box, the ratio of the number of brown marbles to the number of black marbles was 1 : 4. Each time, 3 brown and 6 black marbles were taken out of the coin box. A while later, only 108 black marbles were left in the coin box. What was the total number of marbles in the coin box at first?

	Brown marbles	Black marbles
Before	1x3 = 3 u	4x3 = 12 u
Change	- 3 u	- 6 u
After	0	108

Since there is no brown marbles left, this means that the number of brown marbles at first is the same as the number of brown marbles taken out.  

Make the number of brown marbles at first and taken out the same.  LCM of 1 and 3 is 3.

Number of black marbles in the end
= 12 u - 6 u
= 6 u

6 u = 108

1 u = 108 ÷ 6 = 18

Total number of marbles in the coin box at first
= 3 u + 12 u
= 15 u
= 15 x 18
= 270

Answer: 270