To determine which terms in the expression 3a - 4 + 6ab - 2a can be combined with -4a, we need to first simplify the expression by combining like terms:
3a - 4 + 6ab - 2a = (3a - 2a) + 6ab - 4 = a + 6ab - 4
Now we can see that the only term that can be combined with -4a is the "a" term, since it has the same variable and same exponent as -4a. Therefore, the answer is that only one term in the expression can be combined with -4a.