Answer:
$100
Step-by-step explanation:
The reason is that the minimum value that the buyer of the put option will have is its exercise price because if I have right to sell an asset with exercise price of $100 and the market value of the underlying asset goes below $100 say $90, then I will prefer exercising the option and will receive $100. But suppose if the market price of the underlying asset goes above exercise price and is say $110 then I will benefit by selling the product in the market by receiving $110 not by exercising the put option and receiving $100.
So we can see from the above scenario, the minimum price that the put option holder can get by exercising the put option is its exercise price, hence $100 is the right answer.