x + 997 = 998
145 – x = 143
18 : x + 15 = 18
4 ∙ x + 5 = 21
25 + 3 ∙ x = 40
18 – 15 : x = 13
x = 2
x = 4
x = 9
x = 3
x = 1
x = 5
x = 6
x = 8