This is a linear relationship. The slope-intercept form of the linear equation is:

Where,
- m is the rate of change (positive if increasing rate and negative if decreasing rate)
- c is the y intercept, or the initial value
<u><em>Rate of change is 2.5 quarts per minute (it is decreasing so m is -2.5)</em></u>
<u><em>Initial value is 50 quarts, so c is 50.</em></u>
Plugging in the values we get
.
Changing variables to w instead of y and t instead of x, gives us,
. Where w is warts of water left in the tub and t is the time in minutes.
There is no viable solution when t=30 because at t=20, w=0 (
). It means after 20 minutes, there is no water left. So t=30 minutes doesn't make sense.
ANSWER:
Modelling equation: 
When
, there is no VIABLE solution

seperable differential equations will have the form

what you do from here is isolate all the y terms on one side and all the X terms on the other

just divided G(y) to both sides and multiply dx to both sides
then integrate both sides

once you integrate, you will have a constant. use the initial value condition to solve for the constant, then try to isolate x or y if the question asks for it
In your problem,

so all you need to integrate is
There are no solutions to the given system of equations.
Hope this helps.
The answer is C.
Because it is closest location relative to the sea!