If the box is truly a cube, then all 3 of its dimensions are the same . . . the cube root of 90. There's no "might" about it.
Eight and two hundred sixty one thousandths
You are correct. 4 is the slope and 2 is the y intercept.
Reasoning:
y = mx + b is the slope intercept form of a line
m stands for slope
b stands for y intercept
In your case, m = 4 and b = 2.
By De Moivre's theorem,

We can stop here ...
# # #
... but we can also express these trig ratios in terms of square roots. Let
and let
. Then recall that



On the left,
so that

Since
, we're left with

because we know to expect
. Then from the Pythagorean identity, and knowing to expect
, we get

Both
and
are
-periodic, so that

and

so that the answer we left in trigonometric form above is equal to

6x-7=4x+7
6x=4x+14
2x=14
x=7