Now all of this could be calculated from first principles, going down into the trigonometry. Thankfully, EASA do not expect us to be able to do trigonometry on the approach, so we have useful shortcuts and "rules of thumb" to use.

One such rule is that:

Rate of Climb/Descent (ft/min) = Groundspeed (nm) x Gradient (%)

This is an approximation but is actually very close, so very useful for us in many questions.
We can make this question even easier still, as a 3º glide path is the most common for approaches.

3º is equivalent to a gradient of 5%, so the RoD = 5 x Groundspeed. This is the same for every 3º glide path of course, so very useful to remember.

RoD = 120 x 5 = 600 ft/min.