One type of liquid contains 10% of water and the second type of liquid contains 15% of water. A glass is filled with 5 parts of 1st liquid and 2 parts of 2nd liquid. The percentage of water in the new mixture in the glass is?
Choose the most appropriate option.
A) 5.6 %  B) 11.4 %  C) 15.6 %  D) 21.3 %  E) 18.9 %

Rationale: "required percentage = ( 10 % of 5 + 15 % of 2 ) / 5 + 2 * 100 = 0.8 / 7 * 100 = 11.4 % answer is b"
Answer: B