6 is the amount of hotdog buns needed.
You subtract 12 from 18 because you already have that amount of buns and need to see how many you need to get.
Given : Joe is preparing 18 hot dogs for his party.
He has 12 hot dog buns.
To Find: how many more hot dog buns does Joe need?
Joe is preparing hot dogs = 18
He has hot dog buns = 12
So, more hot dog buns required =18-12
No. of hot dog buns required more = 6
Hence Joe need 6 more hot dog buns .
6 hot dog buns
Total number of hot dog buns required by Joe = 18
Total number of hot dog buns with Joe at present = 12
Thus, Joe has lesser number of hot dog buns as required.
The number of hot dog buns required over and above 12 hot dog buns
= Hot dog buns required - Number of hot dog buns with Joe at present
18 - 12 = 6
Joe still needs 6 hotdog buns.
18 hotdogs - 12 hotdog buns = 6 hotdug buns still needed
Since Joe's starting amount of hot dogs is 18, we know he will need that many buns.
Since he currently has 12, we can subtract that number from the total amount he needs.
Amount he need - Amount he had = Amount more he needs to buy.
18 - 12 = Amount more he needs to buy.
6 = Amount more he needs to buy.