having trouble explaining this

Question

at a flower shop, Teri sees that roses are $3 each, carnations are $4 for 3 flowers, and tulips are $4 for 4 flowers. She buys 3 roses and 3 carnations. She has $20. How much change does teri get back

Answer 1

Roses cost $3 each.  Since Teri bought 3, she paid 3*($3) = $9.

 

Carnations are $4 for 3 flowers.  Since Teri bought 3 flowers, she paid $4

 

Teri paid = $9 + $4 = $13

 

Change = $20 - $13 = $7