First let’s let x equal the price of breakfast.
We form the question that 20 percent of x is 1.80
We also know that 20% = 0.2
Now let’s write this as a mathematical equation:
0.2 x = 1.8
Let's divide both sides by 0.2 so that we can isolate the x:
x = 1.8 / 0.2
= 9
No way we know that the price of breakfast before the tip was $9
I hope this helped! :)