7 cups of flour ... 9 people
x cups of flour = ? ... 15 people
If you would like to know how many cups are needed to make a cake for 15 people, you can calculate this using the following steps:
7 * 15 = 9 * x /9
x = 7 * 15 / 9
x = 35/3
x = 11 2/3 cups of flour
Result: 11 2/3 cups of flour are needed to make a cake for 15 people.