Question 164902
4x^2 - 6x^3 + 3x^4 - 5x^2 - 7x^4 + 6x^3
= 3x^4 - 7x^4 - 6x^3 + 6x^3 + 4x^2 - 5x^2       
= -4x^4 - x^2


I hope you will ubderstand this
for your convenience i ad placed like terms aside in the 2nd line