First you got to find the Greatest Common Factors or GCF of the denominators or 4 and 5 which is 20. Then, you multiply each side by the number that when multiplied gives you 20 (in this case its each other). 3/4 is now 15/20 and 1/5 is 4/20. Now to add them is quite simple, you're going to add the numerators which gives us a grand total of 15/20+4/20=19/20 in simplest terms.