If there is a 5% drop every month, then the class becomes 1-5%=1-0.05=0.95 times the previous size.
The formula for

months would be

so for 12 months it would be
On the complex plane, the number
is mapped onto the point with coordinates
.
In other words, the x coordinate is the real part of the number, while the y coordinate is the complex part of the number.
Viceversa, if you start from a point
, you can identify the number
.
So, the endpoints of the diagonal are the points
and
. These are points A and C in the attached figure.
This means that points B and D have coordinates

So, the correspondant complex numbers are

The correct answer is 3 inches.
To find this answer, we need to write and solve a quadratic equation.
Let's call the width of the frame X.
Then, the total width is 10 + 2x and the total length is 12 + 2x.
Having this information, we can write and solve the following equation.
(10 + 2x)(12 + 2x) = 288
4x^2 + 44x + 120 = 288
4x^2 + 44x - 168 = 0
4(x - 3)(x + 14) = 0
The solutions are 3 and -14, but only 3 makes sense in the story problem.