Answer:
Daniel is 13 now.
Step-by-step explanation:
3 years ago, the difference between Ben's age and Daniel's age was twice Daniel's age then. That difference was 20 years, so Daniel's age 3 years ago was 10. Daniel is now 13.
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Check
Ben is now 33. 3 years ago, he was 30 and Daniel was 10, so Ben was 3 times Daniel's age then.