I'm trying to place an order on TradingView to buy BNB.

But I wanna spend 0.3 Bitcoin for the trade.
But the platform doesn't give me an option to enter how many bitcoins I wanna trade. Instead, it asks me how many altcoins (BNB) I wanna buy.

So what's the formula for converting say 0.3 bitcoin to a specific altcoin?



Appreciate the help,

JH