What numbers should be subtracted from each of the numbers 23, 30, 57 and 78 so that remainders are in proportion?

If k + 3, k + 2, 3k - 7 and 2k - 3 are in proportion, find k.

What numbers must be added to each of the numbers 16, 26 and 40 so that the resulting numbers must be in continued proportion?

Find two numbers such that the mean proportional between them is 28 and the third proportional to them is 224.