Explanation of single vs double quotation marks

While both single and double quotation marks will print what is between,
there is a proper time to use both. Single quotation marks will treat all values inside literally.
Double quotation marks will treat the values inside with their interpretation.

Using single quotation marks:

When you purchase $quantity bottles of fingernail polish at $$price, with tax it
will cost a total of $$total.

Using double quotation marks:

When you purchase 5 bottles of fingernail polish at $4.59, with tax it
will cost a total of $24.21.