Sir please just explain this to me how to calculate this..question.

Cruising level= 060
Gs= 120
Rod= 500fpm

You are required to reach 3000ft by 10nm from destination. What distance from destination should you commence decend?

t=3000ft÷500ftpm=6 minutes
D= S×T
120×6=720÷60=12 NM

12nm+10nm=22nm

My answer was 22nm

Please just check and help me out.

If 3000' is an altitude, your working is correct.

If 3000' is a height AGL, you will need to account for the aerodrome elevation.

Looks okay, I got 23NM but I used E6B computer and rounded the distance 13NM for the distance covered during the descent.

You state cruising level 060. I think levels normally apply above the transition layer. So unless it was FL 600 in the question, but I don't think it was because that would have to come accompanied with a QNH to allow the same datum to be used for correct measuring of vertical distance required to climb or descend.

I got 23NM but I used E6B computer and rounded the distance 13NM for the distance covered during the descent.

Then you are using your computer incorrectly. Can you take a photo of your settings and post them so we can sort out whatever problems you might be having with its use, please ?

I think levels normally apply above the transition layer.

"level" is just a generic term. It would have been better had the question referred to A060 to make it clearer that the intention was to refer to an altitude rather than a flight level.

Silly me. I misread my E6B. Yes it's 12 and subsequently 22.

Thanks John. Picture included highlighting my silly error!

Good one - always best if you can spot the problems yourself - sticks in the memory cells far more effectively.