The return on capital employed is an accounting measure and uses the accounting profit. The profit before interest and tax is already after charging depreciation, as you should remember from Paper FA (was F3). We do not subtract depreciation again.
The only time we would deduct depreciation would be if we were given the operating cash flow. In this case we would need to subtract depreciation to arrive at the operating profit.
I do suggest that you watch my free lectures on this. The lectures are a complete free course for Paper PM and cover everything needed to be able to pass the exam well.