The simple
solution (and the one expected by the examiner) is the whizz
wheel and the 1 in 60 rule.
For rate of descent put the glide slope angle (in Q4360 this is 3.5º) on the
outer scale next to 60 on the inner scale.
Now go to
groundspeed in knots on the inner scale (150kts) and next to it on the outer
scale you have rate of descent in feet per minute (880 ft/min) and we go to the
best answer on offer: 900 ft/min.
The only assumption we make is that 1nm = 6,000ft but this is the type of
calculation you would make whilst flying using the wondrous nav
computer.