Step-by-step explanation:
4x² -6x⁶+2x³+12-5x³+4x⁴
combine like terms
4x² -6x⁶- 3x³ + 12 + 4x⁴
since nothing else can combine due to no exponents being the same number you now have to put in order from biggest exponent to the smallest
-6x⁶ + 4x⁴- 3x³ + 4x² + 12
