#### Answer

a) $3.4000\times10^{4}$ cm
b) $6.378\times10^{3}$ km
c) $7.4\times10^{-11}$ m
d) $4.6\times10^{5}$

#### Work Step by Step

a) 34,000 cm
Replace the comma four places to the left, so the exponential notation is $3.4000\times10^{4}$ cm.
b) 6378 km
Replace the comma three places to the left, so the exponential notation is $6.378\times10^{3}$ km.
c) 74 trillionths of a meter is the same as $74\times10^{-12}$ m. Replace the comma one place to the left so the exponential notation is $7.4\times10^{-11}$ m.
d) The answer of the sum $\frac{2.2\times10^{3} + 4.7\times10^{2}}{5.8\times10^{-3}}$ is $\frac{2670}{0.0058}$, which is 460,344.8. Replace the comma five places to the left, so the exponential notation is $4.603448\times10^{5}$. Rounding to 2 significant figures gives $4.6\times10^{5}$.