The 4 digit number 13b7 is divisible by 11. Sum of odd numbers - Sum of even number = 0, or 11 (1+b)−(3+7)=0 or 11 1+b−10=0 or 11 b - 9 = 0 or b - 9 = 11 b = 9 or b = 20 rejected because b is a single digit number. Now, 1,397 is 4 digit number. The three digit number is 4a3 added to 984, obtaining 1,397. Value of a = 1,397 - 984 = 4 a 3 9 - 8 = a 1 = a Value of 3a + 4b = 3(1) + 4(9) = 3 + 36 = 39.