

Solve for y

let's put our equation first

Flip the equation

Now follow the rule of 


_________________________

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add
to both sides

Divide both sides by 


would equal 
N and d are both numbers of thousands of dollars.
Thus, if n = 1, that means $1000.
Here n = d + 0.4.
Note that in C, n+0.04=n is completely wrong.
Similarly, in D, d = 0.04 = n is completely wrong.
The "combined profit amount" for Nov. and Dec. is n + d = 3.15.
Only A matches this info. Your answer is A.
Answer: u should have at least i gallon per person per day