Vanessa purchased a bottle of wine. She used ⁴₇ of the wine in April. She then used the remaining wine in May and June in the ratio 1 : 3. Given that the amount of the wine used in June was 0.21 ℓ less than that in April, how many millilitres of wine did the bottle contain at first?

April	May	June	Total
4x4	3x4		7x4
	1x3	3x3
16 u	3 u	9 u	28 u

Total volume of May and June is combined repeated identity. Make the total volume of May and June the same. LCM of 3 and 4 is 12.

Volume of less wine syrup in the bottle used in June than April
= 16 u - 9 u
= 7 u

7 u = 0.21 

1 u = 0.21 ÷ 7 = 0.03

Amount of wine in the bottle at first
= 28 u
= 28 x 0.03
= 0.84 ℓ

1 ℓ = 1000 mℓ

Amount of wine in the bottle at first
= 0.84 x 1000
= 840 mℓ

Answer(s): 840 mℓ