Respuesta :

8 - 3(7-4y)
8 - (3x7 - 3x4y) You need to develop between parentheses bcs there is a minus between 8 and 3.
8 - (21 - 12y)
8 - 21 + 12y /!\ A minus before parentheses changes the sign in the parentheses !
12y - 13

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