I and a friend of mine solved the question together. So here's the solution: In 3.4 nm of DNA there are 10 base pairs. That means, in 64nm DNA there will be a total of 200 base pairs. Adenine is given to be 30%. Adenine binds with thymine so thymine would be 30% too. That makes a total of 120 base pairs(60% of 200 base pairs). Hence Guanine and Cytosine would be 20% each. That's a total of 80 base pairs (40% of 200 base pairs). A binds with T with 2 H bonds and G binds with C with 3 H bonds.