$15,000 … how much BTC can I buy for $84k a bitcoin 

A thought: buying bitcoin while it is on discount!

$1.78M from only $15k investment!!!

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To calculate how much Bitcoin (BTC) you can buy for $15,000 at a rate of $84,000 per BTC:

\text{BTC amount} = \frac{\text{Investment amount}}{\text{Price per BTC}} = \frac{15,000}{84,000} = 0.178571 \text{ BTC (approximately)}

Thus, you can purchase approximately 0.1786 BTC.

Times $10M … 

If you hold 0.178571 BTC and Bitcoin reaches $10,000,000 per BTC, your holding would be worth:

0.178571 \text{ BTC} \times \$10,000,000 = \$1,785,710

Your initial $15,000 investment would become approximately $1,785,710.