Need with this, i dont understand so also explain!

The rule for dividing exponents is:
For exponents with the same base, you can subtract the exponents and put the difference as exponent over the base. Remember that the fraction bar acts as a division sign! Or: 

For example: 

Back to your problem:
You're asked to simplify .

Use your exponent rule for dividing exponents. 

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B12/23 is your answer