Subject: mathqa
Question: solution x is 30 % chemical a and 70 % chemical b by volume . solution y is 40 % chemical a and 60 % chemical b by volume . if a mixture of x and y is 36 % chemical a , what percent of the mixture is solution x ?
Option: 
A: 35 %
B: 40 %
C: 30 %
D: 50 %
Answer: B