1. 몇 means 'how many'. 2. 살 is a counter for 'age'. So it would be 'years old' in English. e.g.제 딸은 세 살이에요. (My daughter is 3 years old.) 3. Here are the examples of 몇 with other counters. 몇 개 (how many items), 몇 병 (how many bottles), 몇 명 (how many people) etc.

2) '이다'