You add/subtract complex numbers simply by adding/subtracting real parts and imaginary parts.
So, the real part of this sum is the sum of the real parts:

And the imaginary part of this sum is the sum of the imaginary parts:

So, you have

Answer: I believe it would be 15.42
Step-by-step explanation:
After 64 days, you will owe
.. 310*(1 +0.18*64/365) = 319.78
You must pay $319.78 on October 15.
Additive inverse is what you add to a number to get zero.
You are given 1.4 so you need to ADD -1.4 to get zero.
h=-1.4