Do not understand Qualifying Loan Interest

Hi Sir/Ms,

I am really confused about the qualifying loan interest to the wording of the text. May I ask a few of the following questions? Thank you in advance for you kind patience. Here they are:

1. The interest benefit is not taxable if the total of all non-qualifying loans to the employee did not exceed £10,000 at any time in the text year.
–> What does it mean by non-qualifying loans? Or qualifying loans as non-qualifying will just be the opposite. Are they a group of loans that fall in a certain of categories, or rather any loans that exceed £10,000 is qualifying?

2. If the interest is only partly eligible for tax relief, then the employee is treated as receiving earnings because the actual rate of interest is below the official rate. {He is also treated as paying interest equal to those earnings. This deemed interest paid may qualify as business expenses or as deductible interest in addition to any interest paid.}
–> I am completely lost on the two sentences in the parenthesis. Could you help me to understand in a straightforward and in a simple English way?

3. Example:
Anna has an annual salary of £30,000, and two loads from her employer:
a). A season ticket loan of £8,300 at no interest
b). A loan, 90% of which was used to buy a partnership interest, of £54,000 at 0.5% interest.
What is Anna’s tax liability for 2015/16?
Solution provided in the text book:
Salary:30,000
Season ticket loan (non-qualifying): nil (not over £10,000)
loan to by partnership interest (qualifying): 1,350 (£54,000 * (3-0.5)%)
Total income:31,350
Less deductible interest deemed paid: (1,458) –> £54,000 * 90% * 3%
Net income: 29,892
Less Personal allowance: (10,600)
Taxable income: 19,292
Tax liability: 3,858 (£19,292 * 20%)

How is loan b) applied in this question? It is qualifying, so how one can find out that its interest is only partly eligible for tax relief? I assume this interest is only partly eligible, right?
And about the deductible interest deemed paid, why is it deductible? How can I see it? also why the interest is 3%, not the 0.5% that was provided?

Thanks.