Suppose you are at a restaurant and your favorite dish costs $20. You are willing to pay up to $17 for your next favorite dish. If your next-favorite dish gives you 100 utils, how many additional utils do you need from your favorite dish to spend the extra $3?

I need an additional 17.646 utils.

Explanation:

Amount I am willing to pay for my next favorite dish is $17

Number of utils that $17 can give me is 100

Therefore, $1 would give me (100 : 17) utils = 5.882 utils

To spend the extra $3, I need an additional utils of (5.882*3) = 17.646