algebra
posted by kate .
1. a number increased by 21 is 28. find the number
2. a number decreased by 12 is equal to 30. find the number.
3. 8 less than a number is 15. fid the number

Let x = the unknown number.
x + 21 = 28
x + 21  21 = 28  21
x = 7
x  12 = 30
x = ?
How do you think you should set up the third problem?