Mass of Mars is $$6.42\times 10^{29}\ kg$$ and mass of the Sun is $$1.99\times 10^{30}\ kg$$. What is the total mass?
The mass of Mars $$=6.42\times 10^{29}\ kg$$
The mass of the Sun $$=1.99\times 10^{30}\ kg$$
Total mass of Mars and the Sun combined
$$=6.42\times 10^{29}+1.99\times 10^{30}$$
$$=6.42\times 10^{29}+19.9\times 10^{-1}\times10^{30}$$
$$=6.42\times 10^{29}+19.9\times 10^{29}\cdots\cdots[\because a^m\times a^n=a^{m+n}]$$
$$=(6.42+19.9)\times 10^{29}\ kg$$
$$=26.32\times 10^{29}\ kg$$