Dropdown select appends value

[IlirBajrami]

I'm having another issue.
When i increase the item quantity in the cart page, for the first product, it adds a "0" in front of the value (for instance, when i select quantity of "5", it adds "05") then when increase it on the second product, it appends the quantity value instead of increasing it.
Here's a screenshot with the code and UI.
*pls note that im not using material UI theme. I'm using simple HTML select

The subtotal result is right though (this the sum for 9 products) but it shows 054items! (the 05 from the first product and the 4 from the second)