Question

7a - {-2a -[-(-(a +3b) - (-2a +5b)] - (-b +3a)} 

Answer 1

Que tienes que hacer ?

Answer 2

7a - {-2a -[-(-(a +3b) - (-2a +5b)] - (-b +3a)}

7a - {-2a -[-(-a -3b +2a -5b] +b -3a)}

7a - {-2a -[-(a -8b)] +b -3a}

7a - {-2a -[-a +8b] +b -3a}

7a - {-2a +a -8b +b -3a}

7a - {-13a -7b}

7a +13a + 7b

20a + 7b