Answer: Martha does not have a dominant strategy
Explanation:
A dominant strategy is one that a player can embark on and get the highest payoff regardless of the actions of their competitor.
In this scenario, there is no strategy that Martha can embark on that would provide the greatest payout regardless of Oleg's decision. If Martha advertises, Oleg makes the same amount advertising as well. If Martha does not advertise, Oleg would decide not to advertise as well and make the same amount.
Martha therefore has no dominant strategy as Oleg would make the same amount regardless of which decision is taken.