B can be eliminated, as 10x and 4x multiply to 40x^2, which is not in the expression.
The greatest common factor of all coefficients in the equation is 2. Divide all coefficients by 2 to get the following equation:

We will leave out this coefficient, 2, for now.
We'll need to find the factors of c:
c = -6
Factors of 6: {1,2,3,6}
The only factors in the answer choices that fit this are 2 and 3. D can be eliminated.
5x and 2x multiply to 10x^2. 5x and 2x also modify what b will equal. Use the answer choices A and C to find b:
A.

C.

Answer C comes up with the correct b value.
The answer is
C. 2(5x - 2)(2x + 3).