Trying to figure out how to calculate a semester grade

Ok so i'm taking a programming class at my school and my instructor has given me some word problems to solve and one of them is asking me to develop a function for a semester-grade out of just a homework score and the final exam score- the semester grade is 80% homework and 20% final exam. I just need to figure out how to use the percentages from each score to calculate the final grade. Would i divide the homework grade by 80% and the test grade by 20%?