This is a nice and simple question.

A 3° glideslope is the standard glideslope used for most ILS approaches. A simple rule of thumb to calculate the required rate of descent in ft/min, is to multiply the GS (in kt) by 5. In this case, we are also just given the Groundspeed:

• 150 kt x 5 = 750 ft/min

For more complicated questions with non-standard glideslopes, we can calculate the required rate of descent (RROD) for a 3° Glideslope, and then correct it based on the steepness of the slope. For example, a 6° Glideslope requires the ROD to be doubled. For other values, we can use the equation:

• RROD = GS x 5 x (Glideslope/3)

Note: The above methods are not exact, they are a useful approximation to calculate roughly what the rate of descent should be to maintain the required glideslope or descent angle based on a certain groundspeed. It seems however in EASA exams that this is the method used to calculate the answers.