The problem
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shouldn't -5y+10y+15y?
Answer provided by our tutors
There is no 'y' factor outside of the parentheses... the factor '5' is multiplied by '-2y' and the negative becomes a factor to change '-10y' into '+10y'. It can also be useful to click on the 'Options' tab and begin a solution with 'a few steps', then click on a particular solution step in order to review the logic which is employed.