Solve the Problem $\frac { \mathrm { dy } } { \mathrm { dt } } = - 0.7 \mathrm { y }$

Multiple Choice

Solve the problem.
-In a chemical reaction, the rate at which the amount of a reactant changes with time is proportional to the amount present, such that $\frac { \mathrm { dy } } { \mathrm { dt } } = - 0.7 \mathrm { y }$ , when $\mathrm { t }$ is measured in hours. If there are $78 \mathrm {~g}$ of reactant present when $t$ $= 0$ , how many grams will be left after 4 hours? Give your answer to the nearest tenth of a gram.

A) 4.7 g
B) 2.4 g
C) 0.1 g
D) 7.1 g