I didn't mean to post the answer and can't figure out how to take it down. Somebody report it so it does go down and the question can be later answered. Thank you
Say that you're thinking of number 
You multiply it by 8, and have 
You add -1 (i.e., you subtract 1) and have 
This equals -17, so you have

Add 1 to both sides

Divide both sides by 8:

So, you were thinking of -2.
nt / (n+t)
substitute n=15 and t=7
(15*7)/(15+7)
105/22
22 goes into 105 4 times with 17 left over
4 17 /22
An onion weighs around 4.34 ounces