Question

What must be added to 3x -7 to make x2 + 4x -1?

Answer 1

The term that can be added is the difference between the two expressions you have:

x^2+4x-1-(3x-7)

x^2+4x-1-3x+7

x^2+x+6

Answer 2

you must add x^2 + x + 6