Răspuns :
a + 3/9 = 8/5
45 a + 15 = 72
45 a = 57
a = 57/45
4/9 + a = 6/9
4+9a = 6
9a = 6-4
a = 2/9
12/14 - x = 6/14
12 - 14x = 6
14 x = 6
x = 6/14 = 3/7
x - 12/19 = 5/19
19 x - 12 = 5
19 x = 17
x = 17/19
45 a + 15 = 72
45 a = 57
a = 57/45
4/9 + a = 6/9
4+9a = 6
9a = 6-4
a = 2/9
12/14 - x = 6/14
12 - 14x = 6
14 x = 6
x = 6/14 = 3/7
x - 12/19 = 5/19
19 x - 12 = 5
19 x = 17
x = 17/19