Actually you are doing things way ahead of whatever is required by the instructions, but I guess you just want to challenge yourself first before reading the next few exercises
Anyway, your code didn't work because of how you wrote it. For example, you wrote:
meal / 100 * 6.75 = tax
Unfortunately, Python is a formal language, so it is really strict on the syntax and stuff. In Python, when you assign a value to a variable such as tax, the assignment binds a name on the left hand side of the operator to the value on the right hand side of the operator.
So, the correct phrasing should be:
tax = meal / 100 * 6.75
Switch all the others around as well, and the code should run fine.