If the elder son is 40 years old now, the younger son is 40-10 = <<40-10=30>>30 years old.

In 30 years from now, the younger son will be 30+30 = <<30+30=60>>60 years old.

# Answer

60
<|im_start|>system
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<|im_start|>user
The difference in age between Declan's elder son and younger son is 10 years. If the elder son is 40 years old now, how old will the younger son be 30 years from now?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
60
The difference in age between Declan's elder son and younger son is 10 years. If the elder son is 40 years old now, how old will the younger son be 30 years from now?
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