What number must be added to each of the numbers 5, 11, 19 and 37 so that they are in proportion?

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

If (x + 5) is the mean proportion between x + 2 and x + 9, find the value of x.

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