Question 825578
{{{(8x^4+7x^6+5-7x^5)-(-6+3x^5+3x^6-4x^4)}}}
{{{8x^4+7x^6+5-7x^5+6-3x^5-3x^6+4x^4}}}
{{{12x^4 + 4x^6 - 10x^5 +6}}}

Then arranged it in descending order exponents. :)

{{{4x^6 - 10x^5 +12x^4 +6}}}