Suppose we write down the smallest positive two-digit, three-digit, and four-digit multiples of 9 What is the sum of these three numbers?

Two-digit multiple: 18

Three-digit multiple: 117

Four-digit multiples: 1116

Answer: 18 + 117 + 1116 = 1251

2-digit multiple ==18

3-digit multiple ==108

4-digit multiple ==1008

The sum ==18 + 108 + 1008 ==1,134