Question 128183
The difference between two quantities is the result of subtracting one from the other.  Specifically, the difference between 5 and 3 is 2 because 5 - 3 = 2.


For your situation, the difference between {{{red(2x^2+4xy-3)}}} and {{{green(x^2-2xy-4)}}} is:


{{{red(2x^2+4xy-3)-green((x^2-2xy-4))}}} 


Now distribute the minus sign and remove the parentheses:
{{{2x^2+4xy-3-x^2+2xy+4}}}


And collect like terms:
{{{red(2x^2)+green(4xy)-blue(3)-red(x^2)+green(2xy)+blue(4)}}}
{{{x^2+6xy+1}}}


Done.