I was solving for a stable equilibrium in a game. I calculated expected payoff of one of the players which came out to be the function $$E= -4pq + 0.1p + 0.2q + 0.7$$ where p is probability of an action by one player and q is the probability of the action by opponent. Now, opponent is trying to minimize this payoff. How to go about it ? I am stuck in the maths part of the problem now.