Tony worked 2 hours a day and is paid $0.50 per hour for each full year of his age. This basically says that he gets a dollar for each year of his age. So if he is 12 years old, he gets $12 a day. We also know that he worked 50 days and earned $630 dollars. If he was 12 years old at the beginning of his working period, he would have earned $12 * 50 = $600. If he was 13 years old at the beginning of his working period, he would have earned $13 * 50 = $650. Because he earned $630, we know that he was 13 for some period of time, but not the whole time, because then the money earned would be greater than or equal to $650. This is why he was 12 when he began, but turned 13 sometime in the middle and earned $630 in total. So the answer is 13 years old. We could find out for how long he was 12 and 13. 12x + 13 (50-x) = $630. Then x is $20 and we know that he was 12 for 20 days, and 13 for 30 days. Thus, the answer is 13.
Hope this helped :D
~Melis
