It can be determined that A+B is the smallest, A+C is the second smallest, B+D is the second largest and C+D is the largest, but B+C and A+D are incomparable in size.
∴A+B=45,A+C=49,B+D=60,C+D=64，
A+D and B+C can't be compared in size, so you need to make assumptions.
When A+D=54 and B+C=55, the solution is A= 19.5, B=25.5, C=29.5 and D=34.5 (irrelevant, omitted).
When A+D=55 and B+C=54, the solutions are A=20, B=25, C=29 and D=35.
So d weighs 35 kilograms, so choose C.
This problem happens to be A+D=54 and B+C=55, which is not the purpose of the problem, so I gave up. Upstairs arbitrarily thinks that B+C=54, which is obviously wrong.