$ 71 \times 10^{-9} + 0/35 \times 10^{-7} = 7/1 \times 10 \times 10^{-9}+3/5 \times 10^{-1} \times 10^{-7} \\ = 7/1 \times 10^{-8}  + 3/5 \times 10^{-8} = 10/6 \times 10^{-8} = 1/06 \times 10 \times 10^{-8} = 1/06 \times 10^{-7}$