aig math (Ms.Sue)
posted by lidia .
At the pet store ruth bought 5 rawhide bones and 3 dog collars.She gave the cashier 90$ and received $6 in chage.If a dog collar costs 3 times as much as a bone find the cost of one dog collar.
My answer is 63 am i right if not please show me why and how.

Your answer is obviously wrong. She bought 3 collars. If she paid 63 for one collar  then she would have paid 189 for three.

so is the answer 21?

Let's check:
(3 * 21) + (5 * 7) = 98
Nope  you're getting closer. 
is it 18.

Let's check.
(3 * 18) + (5 * 6) = 84
Right!!! 
my mother dosen't under how you get 18 can you please explain.

I don't know. I found the right answer by trial and error.
Lidia I'm not a math teacher  so please don't include my name on your future posts. 
cost of bone  x
cost of collar  3x
5 bones + 3 collars = 84
5x + 3(3x) = 84
14x = 84
x = 84/14 = 6
cost of bone = $6
cost of collar = 3(6) = $18 
Thanks, Reiny!
I hope Lidia sees your answer.