In algebra, we begin to see variables or letters that are used to represent numbers. An example of a mathematical expression with a variable is 2x + 3. In the expression 2x + 3, the coefficient of x is number 2, and it means 2 times x plus 3.
The expression would be $0.20 x f. Once you figure out what the 'f' variable stands for, you have to multiply it by $0.20, and you will have your answer.
