Xian and his cousin kai both collect stamps xian has 57 stamps and kai has 80 stamps the boys recently joined different stamp collecting clubs xian's club will send him 12 new stamps per month kais club will send him 8 new stamps per month after how many months will xian and kai have the same number of stamps

Number of Kian´s stamps=57+12x
number of Kai´s stamps=80+8x
x=number of months.

the number of Kian´s stamps must be the same than number of Kai´s stamps, so:

57+12x=80+8x
12x-8x=80-57
4x=23
x=23/4=5.75

The number obtained is decimal, therefore, they never will have  the same number of stamps.
After 6 month, they will have almost similar numbers of stamps , but they never will have  the same number of stamps.

they never will have  the same number of stamps.

21, i'm pretty sure it's right lol

That they are numbers and related to each other.