3 years ago, the age of a father was 21 years more than twice his son’s age. After how many years, from now, will he be twice his son’s age?

3 years ago, the age of a father was 21 years more than twice his son’s age. After how many years, from now, will he be twice his son’s age?
3 वर्ष पहले, पिता की आयु उसके पुत्र की आयु के दोगुने से 21 वर्ष अधिक थी। अब से कितने वर्ष बाद उसकी आयु उसके पुत्र की आयु की दोगुनी हो जाएगी?

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