For the first case:

You should break down the 2^9 and 3^6. Bringing down to the smallest factor. You should start by remembering the power values for smaller numbers

Second question-

12^4 can be broken in 2^8 and 3^4

Hence a+b is 12.

For exponents prime factorization is the key.

Further if you’re facing confusion regarding when to multiply subtract or add powers you could always remember this trick of PMDSMA

Powers multiply

Division subtract

Multiplication add

Hope it helps

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