A deep-sea diver should breathe a gas mixture that has the same oxygen partial pressure as at sea level, where dry air contains $20.9 \%$ oxygen and has a total pressure of $1.01 \times 10^{5} \mathrm{N} / \mathrm{m}^{2} .$ (a) What is the partial pressure of oxygen at sea level? (b) If the diver breathes a gas mixture at a pressure of $2.00 \times 10^{6} \mathrm{N} / \mathrm{m}^{2},$ what percent oxygen should it be to have the same oxygen partial pressure as at sea level?