Special Rate Pool Balancing charge

Hi. I had an issue with the below:

In March 2024, the company sold a long-life asset for £70,000. The long-life asset had been bought for £110,000 in May 2021.

In the Model Answer, it goes:
Special Rate Pool brought forward amount 47,000
Disposal of long life asset:
Balancing charge (50% × £70,000) (35,000)
Deduction from SRP (50% × £70,000) (35,000)
Balance on which to charge WDA 37,000
WDA – 6% of £37,000 (2,220)
Balance carried forward 34,780

Total capital allowances = £(35,000) + £2,220 = £ (32,780).

Now, I was wondering why the balancing charge and why the deduction from SRP and why at 50%.
The 50% is maybe due to super deduction. But I’m confused about these treatments.

I would be grateful if you could please assist me on this.