Question: expansion of product of variables

Please tell me how to do about the following problem to me.

 

g:=(b*y)^k*k*y;

simplify(%);

Then, what I obtained was (b*y)^k*k*y, not (b^k)*k*y^(k+1).

expand of the command brought the same answer not (b^k)*k*y^(k+1).

Please tell me what was wrong to my calculation.

 

Thank you in advance.

 

Taro.

 

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