Correct Answer - Option 3 : 14

**Given :**

When 5a3 is added to 321 it will give us 8b4.

**Calculations :**

Highest number in the form 8b4 divisible by 4 = 884

Now according to the question

5a3 + 321 = 884

5a3 = 563

Comparing both sides we get,

a = 6

Sum of a and b = a + b

⇒ 6 + 8

⇒ 14

**∴ Option 4 will be the correct choice **