2/5 tablespoons of vanilla extract ... 6 muffins
x tablespoons of vanilla extract = ? ... 18 muffins
If you would like to know how much vanilla extract does he need, you can calculate this using the following steps:
x * 6 = 18 * 2/5
x * 6 = 36/5 /6
x = 36/5 / 6
x = 6/5 = 1 1/5
Result: Arthur will need 1 1/5 tablespoons of vanilla extract for 18 muffins.
36 bowls - since with one gallon he can eat 12 bowls (as demonstrated by 1/12), you multiply 12 by 3 to get 36 bowls.
It would be .01 or .0y in your case