ITC Jointly Held

Elton is a higher rate tax payer (but with an adjusted net income of ?100,000). This includes £20,000 of rental income on a property owned entirely by Elton on which he pays tax at 40%, a tax liability therefore of f8,000. David his civil partner has no other income.
Discuss how Elton and David could reduce their income tax liabilities.

Answer:
If Elton transfers a 5% (say) holding in his property to David, they will automatically be treated as jointly owning the property for tax purposes and each will be taxed on 50% of the income. Elton’s tax liability will be reduced by £4,000 (10,000 × 40%) and David’s liability will be computed as:
Property income
Less: Personal Allowance
Tax liabilitv
10.000
(12,570)
nil
nil
This will save the couple £4,000.
If Elton transferred the entire ownership then all the income would be assessed on David and his taxable income of £7,430 (20,000 – 12,570) would be taxed at 20% giving a tax liability of £1,486
compared to Elton’s current tax liability on the property income of £8,000 (20,000 × 40%) achieving a total tax saving therefore of £6,514. The election to transfer £1,260 of the personal allowance from
David to Elton would not be available here as Elton is not just a basic rate taxpayer.

Why did Elton not get PA of 12570 his ANI is less than or equal to 100000. Why is his ITL 8000?
Secondly there’s no indication in question of what amount to transfer, are such question testable in TX? Or is this only for practice?