Input Tax Credit Scheme under Transition Provisions

Good Morning All!
I have a query on Input Tax Credit Scheme under Transition Provisions for Excise paid but not holding duty paid document.

As per the rules, 60% of Input Credit is available if the central tax rate is 9% or more & 40% in other cases. If integrated tax is to be paid, it is 30% and 20%.

Please explain this point with an example.

Suppose, I have a stock of some goods valuing Rs. 100. The excise duty paid @ 12.5% under current tax regime. Now GST applicable is 18%.

Q.1 How we will calculate the amount of Input Tax Credit available under GST?

Q.2. Is this 60% or 40% limit is on Excise Duty already paid or output tax liability of GST?