There were blue, grey and yellow balls in a bottle. Sean put another 7 blue balls and 9 yellow balls in the bottle, then the ratio of the number of grey balls to the number of yellow balls became 4 : 3. Then, he doubled the number of blue balls and removed 27 yellow balls. The ratio of the number of blue balls to grey balls became 2 : 1. He counted and found that there were a total of 63 balls left in the bottle. Find the number of blue balls that he had in the end.

	Blue balls	Grey balls	Yellow balls	Total
Before	4 u - 7	4 u	3 u - 9
Change 1	+ 7		+ 9
After 1	1x4 = 4 u	4 u	3 u
Change 2	+ 1x4 = 4 u		- 27
After 2	2x4 = 8 u	1x4 = 4 u	3 u - 27	63

The number of grey balls remains unchanged. Make the number of grey balls the same. LCM of 1 and 4 is 4.

Total number of balls in the end
= 8 u + 4 u + 3 u - 27
= 15 u - 27

15 u - 27 = 63
15 u = 63 + 27
15 u = 90

1 u = 90 ÷ 15 = 6

Number of blue balls in the end
= 8 u 
= 8 x 6
= 48

Answer(s): 48