3. What did a letter signed by world-famous scientist Albert Einstein communicate to Franklin D. Roosevelt early in the war?

I think the letter was about the first atomic bomb.

Explanation:

''The Einstein–Szilárd letter was a letter written by Leó Szilárd and signed by Albert Einstein that was sent to the United States President Franklin D. Roosevelt on August 2, 1939. ... It prompted action by Roosevelt, which eventually resulted in the Manhattan Project developing the first atomic bombs.''

got the explanation from wikipedia, hope this helps.

the answer is: must pay taxes on profits

since it is considered as a part of your income, profits from investments is eligible for tax payment.

the tax from your investment could be influenced by how long you decided to sell it. united states promotes keeping your investment for long term period. so, the tax rate for investments that you sell in less than one year is typically higher compared to investments that you sell in more than one year period.