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Rain is falling at a rate of:

$$R(t)=4{ e }^{ -0.5t }\text{ gallons/hour}$$

...where $t$ is measured in hours.

At what time is the total change in rainfall $3\text{ gallons}$?

$6.214\text{ hours}$

$0.940\text{ hours}$

$0.892\text{ hours}$

$0.575\text{ hours}$