I bought a sounder in the shopping mall last year.
The reason I bought it there is that the brand shop I want is in the mall.
I spent a lot of money on buying it.
But I am very satisfied with it.

*******Correction for Jerome's homework*********
1.
Jerome: I bought  a sounder
correct: I bought a speaker

Explanation:
We don't have the word "sounder". It is appropriate to use the word "speaker" instead.

2.
Jerome: I spent a lot of money on buying it.
        But I am very satisfied with it.
correct: I spent a lot of money on buying it but I am very satisfied with it.

Explanation:
Since you use the coordinating conjunction "but" in your sentences, it is better to write it as one sentence instead. Coordinating conjunction like "but" is use to connect two sentences that shows contrast with the 1st sentence.

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Good day Jerome!

Thank you for submitting your homework. You are so dedicated with your study and you pass your homework all the time. Kindly check few of your corrections to help you improve your English writing skills better. Other than that, you did well! See you in class!

Always,
Teacher Serene