As the current collection period is 59.31 days, you simply assume that this represents 59 days of sales If this is reduced to 30 days and 29 days-worth of sales will be received:
29 x 260/59 = 128
Similarly, reducing to 40 days releases 19 says worth (ie 19 days’ more sales proceeds received)
19 x 260/59 = 84
There are some rounding differences somewhere in the model answer, but the above shows the principle.