1)a+b+c-(a-b-c)=?
2)7 (2a-5b)-5 (3b-4a)

1) 2b+2c или 2(b+c) 2)34a+50b

1) a + b + c - (a - b - c) = a + b + c - a + b + c = 2b + 2c = 2(b + c).2) 7(2a - 5b) - 5(3b - 4a) = 14a - 35b - 15b + 20a = 34a - 50b