To add two fractions with different denominators you need to find a common denominator, usually the lowest you can find. In this case just multiply 3 by 16=48, so 48 is the common denominator. So both fractions can be expressed as a number divided by 48. 1/16=3/48 and 1/3=16/48.
So 13/16=13×3/48=39/48 and 2/3=2×16/48=32/48.
Now the problem is simplified. 39/48+32/48. Because the denominators are the same we just add the numerators: (39+32)/48=71/48.