35x^5+12x^3-36x^4+40x^6+15x^4-45x^5+16x^3+6x-18x^2 combine like terms
The expression is,
35x^5 + 12x^3 - 36x^4 + 40x^6 + 15x^4 - 45x^5 + 16x^3 + 6x - 18x^2
ordering the expression by index,
40x^6 + 35x^5 - 45x^5 - 36x^4 + 15x^4 + 12x^3 + 16x^3 - 18x^2 + 6x
adding together terms of the same index (power),
40x^6 + (35 - 45)x^5 - (36 - 15)x^4 + (12 + 16)x^3 - 18x^2 + 6x
40x^6 + 10x^5 - 21x^4 + 28x^3 - 18x^2 + 6x