Find $h(x)$, with terms in order of decreasing degree, if\[3x^4+2x-1+h(x)=5x^2-6x-1.\]

3x⁴ + 2x - 1 + h(x)  =  5x² - 6x - 1

 

Subtract 3x⁴ from both sides:  2x - 1 + h(x)  =  - 3x⁴ + 5x²​ - 6x - 1

Subtract 2x from both sides:          -1+ h(x)  =  - 3x⁴ + 5x²​ - 8x - 1

Add 1 to both sides:                              h(x)  =  - 3x⁴ + 5x²​ - 8x