Two covalently bonded atoms share a pair of electrons in their outer shell. Each atom contributes one electron to an electron pair, basically adding one electron to their outer shell in the process.
What is your question regarding Xenon?

C=constant
V=variable
Arbitrarily, let's assign a value of 1/2 or 0.5 (however you want to notate 50%) for your percentage/fraction.
C=V/2
or C=0.5V
Isolate the variable to one side. V=2C
Plug in whatever values you know (you should know the constant and the fraction)...

I am guessing you mean 15/sin30=b/sin100
Use simple arithmetic to isolate the variable on one side of the equation:
Multiply both sides by sin100: 15sin100/sin30=bsin100/sin100
b=15sin100/sin30

I am assuming that the terms are (3x), (9/2x), (-6), (4x), (4/x), and (3). It was unclear in the notation if this was the case.
Each term in one parenthetical quantity must be multiplied by each term in the other parenthetical quantity.
12x2+12+9x+18+(18/x)+(27/2x)-24-(24/2x)-18
Group...

On Cartesian coordinate system, your X values (independent variable) will be years. Y values (dependent variable) will be acreage.
This is a span of 92 years (2000-1908), with a change in acreage of 4 acres (5 acres-1 acre).
4 acres/92 years=0.043 acres/yr
*
A constant rate...