Answer:
b. 4x^2 -7x +5
Step-by-step explanation:
When you know a sum and one of its contributors, you can find the other by subtraction. The other trinomial is ...
(7x^2 -5x +4) - (3x^2 +2x -1)
= (7 -3)x^2 +(-5 -2)x +(4 -(-1))
= 4x^2 -7x +5 . . . . . matches B