Scientific notation and operations with numbers

Scientific notation and operations with numbers

[Maximum mark: 4]Scientific notation has the form $a\times10^k$, where $1\leq |a|<10$ and $k\in\mathbb{Z}$.(a) Write $68\,400\,000$ in scientific notation.[1](b) Write $0.000000507$ in scientific notation.[1](c) Write $7.026\times10^{-4}$ in ordinary decimal notation.[1](d) Write $-3.8\times10^5$ in ordinary decimal notation.[1]