John caught 4 fish that weighed a total of 252 lbs. the kingfish weighed twice as much as as the amberjack and the white marlin weighed twice as much as the kingfish. the weight of the tarpon was 5 times the weight of the amberjack. how much did each fish weigh.

Assuming : k=weight of kingfish, a=weight of amberjack, m=weight of white marlin, t=weight of tarpon
The sum of all four fish is 252, so k+a+m+t=252
the kingfish weighs twice as much as the amberjack, so 2a=k.
the marlin weighs twice as much as the kingfish, so 2k=m.
the tarpon weighs 5 times as much as the amberjack, so 5a=t.
Replace the terms k, m, and t: 2a+a+2k+5a=252. k=2a so 2a+a+2(2a)+5a=252. Combine like terms: 8a+4a=252, 12a=252. Divide both sides by 12: a=21. The amberjack weighs 21 pounds. From this, figure out the rest: k=2a=2(21)=42, m=2k=4a=4(21)=42, t=5(21)=105.
Concluding answer - The weights are: amberjack, 21 lbs; kingfish, 42 lbs; white marlin, 84 lbs; tarpon, 105 lbs.