$\begin{array}{11} (a)\; (3 \times 10^5 + 4 \times 10^4 + 8 \times 10^3 + 7 \times 10^2 + 9 \times 10^1) + (5 \times 10^3 + 4 \times 10^2 +8 \times 10^2 + 0 \times 10^1) = (4 \times 10^5 + 0 \times 10^4 + 3 \times 10^3 +5 \times 10^2 + 9 \times 10^1) \\ (b)\;(3 \times 10^5 + 4 \times 10^4 + 8 \times 10^3 + 7 \times 10^2 + 9 \times 10^1) + (5 \times 10^3 + 4 \times 10^2 +8 \times 10^2 + 0 \times 10^1) = (4 \times 10^4 + 0 \times 10^3 + 3 \times 10^2 +5 \times 10^1 + 9 \times 10^0) \\ (c)\; (3 \times 10^5 + 4 \times 10^4 + 8 \times 10^3 + 7 \times 10^2 + 9 \times 10^1) + (5 \times 10^4 + 4 \times 10^3 +8 \times 10^2 + 0 \times 10^1) = (4 \times 10^5 + 0 \times 10^4 + 3 \times 10^3 +5 \times 10^2 + 9 \times 10^1) \\ (d) \;(3 \times 10^4 + 4 \times 10^3 + 8 \times 10^2 + 7 \times 10^1 + 9 \times 10^0) + (5 \times 10^3 + 4 \times 10^2 +8 \times 10^1 + 0 \times 10^0) = (4 \times 10^4+ 0 \times 10^3 + 3 \times 10^2+5 \times 10^1 + 9 \times 10^0)\end{array}$
