Arrange the solutions of the mathematical expressions from least to greatest according to the values in scientific notation 

Quick translate "x is 12 units from 20" into an equation. what are the values of x being described? if you can answer any of my other questions that'd be great too

Write numerical coefficient of y² in the expression 2x² - 15xy – 7y²

Bring the fraction a/a-4 to a denominator of 16-a^2