Three friends, Nakobe, Mikah, and Ashton, are saving up money to buy microphones for their podcast. The total cost of the microphones is represented by the expression;

9x^2 - 3x +

The friends have already saved the following amounts:

Nakobe: x^2
Mikah: x − 12
Ashton: 3x + 4

Which expression represents the amount of money the friends still need to buy the microphones?

A: 8x^2 - 7x - 4
B: 8x^2 - 7x + 12
C: 4x^2 + 5x + 4
D: x^2 + 4x - 8