Almost There, Dude

Mad props to you, yo. You have made it this far. Serious respect. Good luck with this clue. You are going to need it. 

First Problem: k(x)=x^2-12x+75

A. x= -6

B. x= -12

C. x= 12

D. x= 6

Second Problem: m(x)=4x^2+16x+201

A. x= -4

B. x= -2

C. x= 4

D. x=2

Third Problem: n(x)=-6x^2-36x-7

A. x= -3

B. x= -6

C. x= 6

D. x= 3