#### Answer

(a) $6.93*10^{7}$
(b) $7.2*10^{12}$
(c) $2.8536*10^{-5}$
(d) $1.213*10^{-4}$

#### Work Step by Step

(a) $69,300,000=6.93*10^{7}$. Move the decimal point 7 spaces to the left.
(b) $7,200,000,000,000=7.2*10^{12}$. Move the decimal point 12 spaces to the left.
(c) $0.000028536=2.8536*10^{-5}$. Move the decimal point 5 spaces to the right.
(d) $0.0001213=1.213*10^{-4}$. Move the decimal point 4 spaces to the right.