Answer:
-7.1
Step-by-step explanation:
It would be in a state of loss because the units manufactured neither reaches nor exceeds the break even point.
When x=-1:

Ok that gives us a little more information.
If we implicitly differentiate with respect to t, from the very start, then we can apply our product rule, ya?

The right side is zero, derivative of a constant is zero.
Where x' is dx/dt and y' is dy/dt.
From here, plug in all the stuff you know:
y' = -3
x = -1
y = 4
and solve for x'.
Hope that helps!
The interest figure always means the interest for a year.
120 days is 1/3 of a year, so you'll only earn 1/3 of 6.5% .
6.5% = 0.065
1/3 of that is 0.02167 .
(0.02167) x (7,000) = 151.67