Answer:
B. 7x - 5
Step-by-step explanation
Given the expression 21x^2 + 13x – 20, to get which of the given expression is a factor we will have to factorize the equation first as shown;
21x^2 + 13x – 20
= 21x^2 + 28x - 15x - 20
= 7x(3x+4) -5(3x+4)
= (7x-5)(3x+4)
Hence one of the factors is 7x - 5