If you would like to know how many cups of water will Sam need for 6 brownies, you can calculate this using the following steps:
13 brownies ... 1/3 cup of water
6 brownies ... x cup of water = ?
13 * x = 1/3 * 6
13 * x = 2 /13
x = 2/13 cup of water
The correct result would be 2/13 cup.