Quotes

This first set is using single quotes. $num1 is a variable. For reference, $num1 is 10 and $num2 is 25.

Single quote reads everything as a string like in JavaScript and Python.

This second set is using double quotes. 10 is a variable. Because we are using double quotes, it recognize the variable.

Double quotes can read the string and if a variable have been assigned, it would output the variable like the one above.