When an issue creates disagreement among the states, how does federalism solve the problem?

Each state is allowed to make its own decision about the issue. Federal and state powers are equal, so the issue has to be debated. Since federal powers are superior, the Constitution is applied.

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.

i believe your answer is d)