In Revit Electrical, Demand Factors are applied through Load Classifications to compute an Estimated Demand Load rather than simply summing connected loads. The documentation states: ''You use demand factors to adjust the rating of the main service... Demand factors are assigned to load classifications, and load classifications are assigned to device connectors. The estimated load for a device is calculated by multiplying the load by the demand factor. ... The panel schedule can also display the load for each load classification.''

In the exhibit's Demand Factor definition (for the Motor classification), the Calculation method is By quantity with Total at one percentage selected. Two quantity ranges are defined: 0--5 items at 100% and 5--unlimited at 50%. An additional checkbox adds an extra fixed load of 5000 VA to the calculated result. (This follows Revit's behavior of applying the selected demand factor to the connected load and then adding any specified additional load to the result for that classification.)

Panel B feeds only panels E and F. The connected motor loads downstream are:

Panel E: 20 kVA + 10 kVA = 30 kVA

Panel F: 5 kVA + 5 kVA + 10 kVA = 20 kVA

Total connected motor load on B = 30 + 20 = 50 kVA (five items).

Because five items fall in the 0--5 range at 100%, the demand factor is 100% 50 kVA. Per the definition, add an additional load of 5000 VA (5 kVA) to the calculated result:

Demand Load on Panel B = 50 kVA 100% + 5 kVA = 55 kVA.

Therefore, the correct choice is 55 kVA.

References: Revit MEP Electrical documentation -- Demand Factors (assignment to load classifications, multiplication to compute estimated load, and display in panel schedules).