The missing value is also 3/7, because if there was infinitely many solutions, then the two sides of the equation will equal each other.
Hope this helped!!
Answer:
1/8 of the whole pasta or 1/2 of what's left
The payment would be $198.01 and the total interest would be $1,880.75. Pretty straightforward with a financial calc. I can show you the keystrokes if you want, just message.
