The mixture is prepared by mixing two type of tea and it's cost is Rs. 18 per kg. The cost of 1st type of tea is Rs. 15 per kg while the cost of 2nd type of tea is Rs. 20. Find the ratio in which these two types of tea mixed to produce the mixture.
1
2 ∶ 3
2
1 ∶ 3
3
3 ∶ 4
4
4 ∶ 5