Final answer:
The expression 3a - b can be evaluated by substituting the given values of a and b, which are a = 4 and b = 2. The final answer is 10.
Step-by-step explanation:
The expression 3a - b can be evaluated by substituting the given values of a and b, which are a = 4 and b = 2. So, we have 3 * 4 - 2.
Multiplying 3 and 4 gives us 12, and subtracting 2 from it gives us the final answer of 10.