what is the difference and similarities

if solving an equation with varibles in the equation if it had 1 or 2 or even 3 variables?

Here is one:

Money left in Wallet= money earned + money found - money lost - money spent.

I don't understand? can you please explain...

2 answers

Cindy spends 20% of the money that she has on groceries.

She has a total of $30.

How much money did she spend on groceries?
20% of $30
=30 * 1/5
= $6