To solve this you need two separate equations for Xian and Kai. Let's say x represents the number of months.
Xian's equation would be: 12x + 56
Kai's equation would be: 8x + 80
To find out when they'll have the same number of stamps, all you need to do is set both equations equal to each other, then solve. So:
12x + 56 = 8x +80 (subtract 8x from both sides)
4x + 56 = 80 (subtract 56 from both sides)
4x = 24 (divide both sides by 4)
x = 6 They will have the same number of stamps after 6 months.
Now that you have that, you plug in the 6 into either one of the separate equations to find out how many stamps they will both have.
Plugging it into Xian's equation: 12(6) + 56 = 72 + 56 = 128
Plugging it into Kai's equation: 8(6) + 80 = 48 + 80 = 128
So both Kai and Xian will have 128 stamps after 6 months.
