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Probably this can only be done by defining some auxiliary function(s), or importing such functions.

My one-line solution using the (standard) itertools library:

sage: import itertools
sage: reduce(lambda z, w: w, itertools.takewhile(lambda x: x[1] <= 0.4, itertools.accumulate(reversed(D), lambda a, b: [a[0] + b[0], a[1] + b[1]])))
[16800.0000000000, 0.333200000000000]

Here,

• reversed(D) allows iterating over the list in reverse,
• itertools.accumulate allows accumulating a running total,
• itertools.takewhile allows stopping when the accumulated percentage reaches some value,
• reduce is used with lambda z, w: w as a trick to get the last element.