When Javier writes 40 on both accounts they cost him the same amount of money so it should be 41.
Javier needs to write 41 checks for the second bank to beat better
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.
Isolate the variable by dividing each side by factors that don’t contain the variable.
X = -2
Hope this helps!
Have a great day!
I don’t know if this is a joke or not but the answer is 6