Challenge Express each answer in scientific notation in the units indicated.
a. $\left(1.26 \times 10^{4} \mathrm{kg}\right)+\left(2.5 \times 10^{6} \mathrm{g}\right)$ in kg
b. $(7.06 \mathrm{g})+\left(1.2 \times 10^{-4} \mathrm{kg}\right)$ in $\mathrm{kg}$
c. $\left(4.39 \times 10^{5} \mathrm{kg}\right)-\left(2.8 \times 10^{7} \mathrm{g}\right)$ in $\mathrm{kg}$
d. $\left(5.36 \times 10^{-1} \mathrm{kg}\right)-\left(7.40 \times 10^{-2} \mathrm{kg}\right)$ in $\mathrm{g}$