Răspuns :
21 : 3x = 7
21 = 3x * 7
21 = 21x
x = 21 : 21
x = 1
42 : 2x = 7
42 = 2x * 7
42 = 14x
x = 42 : 14
x = 3
21 = 3x * 7
21 = 21x
x = 21 : 21
x = 1
42 : 2x = 7
42 = 2x * 7
42 = 14x
x = 42 : 14
x = 3