function [F] = static_trans_SecondA(x,v2,p,W_a4)

        W_b4 = x(3);
        K_a1 = p(9);
        K_a2 = p(10);
        K_w =  p(11);
        H_plus = v2;

        %F = W_b4*(K_a1/H_plus + (2*K_a1*K_a2)/H_plus^2)/(1+K_a1/H_plus+K_a1*K_a2/H_plus^2)+...
        %    W_a4+K_w/H_plus - H_plus;
        
        num = K_a1/H_plus + 2*K_a1*K_a2/H_plus^2;
        den = 1+K_a1/H_plus + K_a1*K_a2/H_plus^2;
        A = W_b4*num/den;
        B = W_a4;
        C = K_w/H_plus;
        D = -H_plus;
        
        F = A+B+C+D;
    end
