good evening! Can someone please answer this, ill give you brainliest and your earning 50 points. Would be very appreciated.

Step-by-step explanation:
I wrote the steps step-by-step for you
I hope you understand...
Answer:
Step-by-step explanation:
3x^2 + 8x - 16 - SOMETHING = x^2 - 4
Re-arranging left and right:
SOMETHING = 3x^2 + 8x - 16 - x^2 + 4
= (3x^2 - x^2) + 8x - 16 + 4
= 2x^2 + 8x - 12