Subject: mathqa
Question: salad dressing p is made up of 30 % vinegar and 70 % oil , and salad dressing q contains 10 % vinegar and 90 % oil . if the two dressings are combined to produce a salad dressing that is 20 % vinegar , dressing p comprises what percentage of the new dressing ?
Option: 
A: 60 %
B: 50 %
C: 30 %
D: 40 %
Answer: B