In this case simply cross multiplying will help:
$44,000 USD $100 USD
----------- = --------------
1 Bitcoin x Bitcoin
44,000x = 100
Alternatively you can divide 1/44,000 and then multiply by 100. Your answer will be around 0.002272 BTC
To check your answer, take your 0.002272 and multiply it by $44,000 to get back to the $100 investment.
Hope this helps. Good luck.