car lease corporation tax

I faced a confusing question while doing a question in exam kit.

In the solution, it said that when the company has leased the motor car, which has emission rate of 300g/km, and provided to the employee, 15% of annual cost for car lease is not deducted from corporation tax.

I hope it makes sense.

However, I don’t recall learning this percentage.
Could you please explain or point towards a section of course note where I can find this information?

Thank you so much for your help!