If every line parallel to two lines intersects both regions in line segments of equal length, then the two regions have equal areas. In the case of your problem, every line parallel to the bases of the two parallelograms will intersect them in lines segments, each with a width of ℓ.
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.
