In the sandwiches mode, select the "cheese" option and observe the equation given for the preparation of a cheese sandwich. when the number of bread slices and cheese slices is set to "0," you will see that there is "no reaction." now, in the equation, set the number of bread slices to "2" and the number of cheese slices to "1." you will see that the product formed by these three elements is one cheese sandwich with two slices of bread and one slice of cheese.