Billy's age is 30/3 = <<30/3=10>>10 years old.
The sum of the ages of Billy and Lucas is 30/2 = <<30/2=15>>15.
So, Lucas is 15 - 10 = <<15-10=5>>5 years old now.
Therefore, Lucas will be 5 + 3 = <<5+3=8>>8 years old three years from now.
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