Tìm x: a) 1998 + x = 2019

a) 1998 + x = 2019

            x = 2019 – 1998

            x = 21

f) x + 30100 – 15100 = 60000

x + 30100 = 60000 + 15100

x + 30100 = 75100

x = 75100 – 30100

x = 45000

b) x – 3486 = 39401

x = 39401 + 3486

x = 42887

g) 100000 – 30000 – x = 58000

                 70000 – x = 58000

                  x = 70000 – 58000

                  x = 12000

c) x ´ 8 = 67400

x = 67400 : 8

x = 8425

h) x × 8 + 25 = 81

     x × 8 = 81 – 25

     x × 8 = 56

     x = 56 : 8

     x = 7

d) x : 5 = 12300

     x = 12300 ´ 5

     x = 61500

i) 72 – x : 4 = 16

            x : 4 = 72 – 16

            x : 4 = 56

            x = 56 ´ 4

             x = 224

e) 100 000 : x = 5

                x = 100000 : 5

                x = 20000

k) x : 4 × 7 = 25200

     x : 4 = 25200 : 7

     x : 4 = 3600

     x = 3600 ´ 4

      x = 14400