Hello! For your first sentence, 'that' can be removed as it is a repeat of the word 'but' in meaning. For the second sentence, 'that' is used as it points to the subject of the sentence but it is not actually needed to link the sentence together.
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May 6, 2018
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Hello! When you are comparing something to another object there are several ways to describe the similarities and for your correction of 'as you did in my class' to 'that you did in my class' is grammatically correct, great catch!
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May 6, 2018
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Hello! A decade equals ten years time so from 2010 to 2020 is a decade