Answer: Option 1: 6ab
Step-by-step explanation: An operation must have some kind of mathematical 'action' going on. In this case, we see multiplication: the 6 is being multiplied by a and the product of 6 and a is being multiplied by b. We know this is multiplication because we can imagine multiplication symbols between the numbers; when a number and variable or variable and variable are next to each other, it means they are being multiplied.
