8 years ago James had 20-8=<<20-8=12>>12 years
So 8 years ago John had 12*2=24 years experience
That means John has 24+8=<<24+8=32>>32 years experience
So Mike has 32-16=<<32-16=16>>16 years of experience
So together they have 20+32+16=<<20+32+16=68>>68 years experience
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