deferred tax question

On the first day of the accounting period Cold enters into a three-year lease for an asset that
has a cash price of $20,000. The asset has an expected useful life of 10 years. Cold has an
option to extend the lease after three years for a further two years on normal commercial
terms. Under the terms of the lease the rentals payable in the first year are $4,000 and
thereafter $2,000 per year. In the draft accounts an expense has been charged with the cash
paid and no asset or liability has been recognised.
In addition, given a tax rate of 30%, determine the deferred tax implications of the correct
accounting treatment if tax relief will only be granted on the cash payments.

I dont understand the answer where it says we expense 1/3rd of 8k and the difference of 1333 should be taxed at 30% – why arent we expensing the 4k which we paid?

any advise is much appreciated