d. $6 a^{2}-13 a+6$

Step 1 ：Given the quadratic expression: \(6a^2 - 13a + 6\)

Step 2 ：Factor the expression manually: \((2a - 3)(3a - 2)\)

Step 3 ：\(\boxed{(2a - 3)(3a - 2)}\) is the factored form of the given quadratic expression