To add fractions, they must have a common denominator. To set one, find a common multiple of both denominators. Simply multiply them together if it proves difficult.
7 x 39 = 253
Now set the denominators to this number and multiply the numerators by the opposite fraction's denominator.
39/259 + 7/253 = 46/253
This simplifies to 2/11
So, 1/3 + 1/39 = 2/11