Which value from his calculation most strongly affects the number of significant figures in the answer?

Well, the value that would most affect it is the one with the least sig figs

that would be the one that had the least precise way of measurement

What does that mean you dum bum

So what you would do is go through and add 3 teaspoons(tsp) 6 times because of the 6 tablespoons(tbsp). which will give you an answer of 18. another way is to multiply 3x6=18.