Final answer:
The correct option is a). Cannot determine the final price of Picasso's painting without the commission rate. The final price includes both the $26 million sale price and the buyer's commission, which must be calculated.
Step-by-step explanation:
The calculation of the final price of Picasso's painting "Femme Assise Dans un Fauteuil" sold for $26 million, considering the buyer's commission, requires additional information about the percentage rate of the commission. The question provided does not specify the commission rate, so it is not possible to determine the final price without that information. Once the rate is known, the commission amount can be calculated by multiplying the rate by the sales price of $26 million, and that amount is then added to the $26 million to compute the final price.