Let us denote the number of tiles by 
.
In the first store, if Darin bought tiles, he would need to spend:
(measured in $)
In the second store, if Darin bought tiles, he would need to spend:
(measured in $)
For the cost to be the same at both stores, it means (measured in $)
Moving
over to the left hand side and changing signs:
tiles
Let's check. If he buys 60 tiles in the first store, he spends:
$0.79×60 + $24 = $47.40 + $24 = $71.40
If he buys 60 tiles in the second store, he spends:
$1.19×60 = $71.40
∴ Darin needs to buy 60 tiles for the cost to be the same at both stores.
In the first store, if Darin bought
In the second store, if Darin bought
For the cost to be the same at both stores, it means (measured in $)
Moving
Let's check. If he buys 60 tiles in the first store, he spends:
$0.79×60 + $24 = $47.40 + $24 = $71.40
If he buys 60 tiles in the second store, he spends:
$1.19×60 = $71.40
∴ Darin needs to buy 60 tiles for the cost to be the same at both stores.