Let X be the original price. Do a 40% increase we get the price: X+0.4X=1.4X Doing a 25% off we get the new price: (1.4X)-0.25(1.4X)=1.05X =X+0.05X. The new prices are 5% increase from the original price.
The whole point of units conversion is to take a value expressed in one set of units (parts per hour) and translate it to a different set of units (parts per week). The rate does not have to involve time.