Rich chooses a 4-digit positive integer. He erases one of the digits of this integer. The remaining digits, in their original order, form a 3-digit positive integer. When Rich adds this 3 -digit integer to the original 4 -digit integer, the result is 6031 . What is the sum of the digits of the original 4-digit integer?
Answer Choices
A. 18
B. 20
C. 22
D. 19
E. 21