Write a method groceryBill that takes a String input of a grocery bill
and returns the subtotal.
Each new item is on a new line, and each line will be in CSV format:
item(String), quantity(Int), price(Double)
"Apples", 3, 2.00
This one line would have a total of 3 * 2.00 = 6.00.
There will be a variable amount of whitespace surrounding the values.
If the passed string is empty, return 0.0.
Otherwise you can assume that the input has at least one entry and that it follows this format.
You will need the String.toInt() and String.toDouble() methods
to turn a String into a Int/Double value.
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