bài 1 : A + B = C - D

        (a + b - 5) + (-b - c + 1) = (b- c - 4) - (b - a)

        a + b -5 + (-b) - c + 1 = b - c - 4 - b + a

        b + (-b) + a - c -5 + 1 = b - b - c + a - 4

       a - c - ( 5 - 1 ) = (-c) + a -4

      a - c - 4 = a - c - 4

Hello every one! I am..........Today, I will talk about Flowers festival in H.C.M city. It's called Nguyen Hue street in district 1. It takes place every Tet holiday for 1 week. It's celebrated by the Committee of H.C.M city. They decorate the streets with many kinds of flowers and lights to tourists came here take photo and watching different types of flowers. They help festival because It's part of the Tet holiday. finally, I fell proud of Viet Nam country.

100-x=50

      x=100-50

      x= 50