Tìm x biết a. 7 × x + 215 = 285 b. x × 6 + x = 77

a. 7 × x + 215 = 285

               7 × x = 285 – 215

               7 × x = 70

                      x = 70 : 7

                      x = 10

b. x × 6 + x = 77

           x × 7 = 77

                 x = 77 : 7

                 x = 11