NO JOKE 100 POINTS MATH EXPERTS (I ANSWERED QUESTION 1 AND 2, I JUST NEED HELP WITH NUMBER 3,4 AND 5

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There are so many items for sale in our world! Some of the items you can buy will appreciate in value. This means that as time passes, the value of the item increases. If you decide to sell the item at a later time, you should be able to sell it for more than you paid. Some common examples of items that appreciate in value include houses, stocks, and some types of art.
Other items you can buy will depreciate in value. This means that as time passes, the value of the item decreases. If you decide to sell the item at a later time, you will likely have to sell it for less than you paid for it. Cars, game systems, and jewelry are examples of items that usually depreciate as time passes. The majority of items that depreciate never reach a value of $0. Their worth attains some minimum, positive value that is greater than $0 and then their price stabilizes.
In 1981, IBM manufactured and sold one of the first personal computers. The machine was called the IBM Personal Computer (PC) 5150 and the full model retailed for $3,000. Similar to modern technology, the value of this item depreciated over time. The function that models how the PC 5150 depreciated as time passed is , where x is the number of years after 1981 and f(x) is the value of the PC 5150.