A human cell has 6.6 × 10⁹ base pairs of DNA…

Step 1. (a) $6.6 \times 10^9 \div 200 = 3.3 \times 10^7$, which is $33$ million nucleosomes.

Step 2. (b) $33 \times 8 = 264$ million histone molecules.

Step 3. (c) $200 \times 0.34\ \text{nm} = 68\ \text{nm}$.

Step 4. (d) $6.6 \times 10^9 \times 0.34\ \text{nm} = 2.244 \times 10^9\ \text{nm}$. Since $10^9\ \text{nm} = 1\ \text{m}$, the length is $2.24\ \text{m}$.