You need to get a common denominator. 3/4= 9/12 because 3x4=12 and 3x3=9. you must do the same thing to both sides. 1/3=4/12 because 3x4=12 and 1x4=4.
2/6=4/12 because 6x2=12 and 2x2=4. 9/12+4/12+4/12=17/12, or 1 5/12. You keep the denominator and add the numerators.
