Answer:
A: 244 pounds
B: 122 pounds
C: 274 pounds
Step-by-step explanation:
We have A+B+C = 640; A=2B; C=A+30. Substituting the last into the first gives ...
A + B + (A +30) = 640
2A +B = 610 . . . . . . . . . . . . subtract 30
Substituting the second into this equation gives ...
2(2B) +B = 610
B = 610/5 = 122 . . . . . divide by 5
A = 2B = 244 . . . . . . . .find A from B
C = A+30 = 274 . . . . . find C from A
Box A weighs 244 pounds; box B weighs 122 pounds; box C weighs 274 pounds.
