The relationship between the number of $4 lunches you buy with a $100 school lunch card and the money remaining on the card

To set up an equation for this you must know what needs to be on the other side of the equals sign or what the answer is supposed to be. In this case, we know the answer should be the money remaining on the card. Since there is no number value for this, you must pick a variable to represent it. I am going to use variable R. So, since we know that you start with 100 dollars, and lose 4 dollars for each lunch, we can tell that there will be subtraction taking place. We also do not know how many lunches have been bought so we need a variable for that too. I will use variable x. That will leave you with an equation of:
R = 100 - 4x

x= number of lunches bought
R= remaining money on the lunch card

Hope this helps!

The answer is