Can’t find an answer to this! someone pls ! 4n+6n-2 = 2(n+3)

Enter the number of complex zeros for the polynomial function f(x) = x 4+ 5x² +6

What would be the reasons for lines 3 and 4? a. addition property; subtraction property b. addition property; solve c. substitution property; subtraction property d. substitution property; prove

Find the vertex for the parabola given by the function ƒ(x) = −3x2 − 6x.