Reverse the sign of each term you are subtracting and then add as usual. Hope this helps!
I'm confused what are you suppose to do
Without the tip it was $60. If you are being asked to add the tip it will be $69
The rice will cost $17.6 for serving 40 people
<h3><u>Solution:</u></h3>
We need to determine the cost of serving 40 people with rice
Arborio rice is purchased in 2-pound boxes for $1.99
The price of 1 pound box will be 
1 Pound (lb) is equal to 16 ounces (oz)
Therefore, the price of 16 ounces is $0.995
A cup of raw Arborio rice weighs 7 ounces and it serve 1 people

Therefore rice will cost $17.6 for serving 40 people
The second equation, its setup is correct