human
Comet Halley orbits the sun every 75 years. Bill's dad saw the Comet when he was 30 years old. Bill saw the comet a second time when he was three times the age his father was when he saw the Comet. How old was Bill when he saw the Comet for the first time?
assistant
How old was Bill when he saw the Comet for the second time? ** Bill saw the Comet for the second time when he was 30 years * 3= <<30*3=90>>90 years old.
How old was Bill when he saw the Comet for the first time? ** Comet Halley can be seen every 75 years, so Bill saw the comet for the first time when he was 90 years - 75 years = <<90-75=15>>15 years old.
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