The correct article is "The". In this context, "The price" refers to a specific price that is being discussed or considered, which requires the definite article "The".
The sentence becomes:
The price must be more realistic if you want to sell this item.
The correct article is "The".
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?