Soppose the elongation in first string be \\\\(x_1\\\\) and in the second string be \\\\(x_2\\\\)Now for second string, in equilibrium\\\\(K_2x_2=m_2g\\\\) or \\\\(x_2= m_2g/k_2\\\\) (1)For first string in equilibrium\\\\(K_1x_1=(m_1+m_2)g\\\\) or \\\\(x_1= (m_2+m_1)g/k_1\\\\) (2)Now potential energy stored will be\\\\(U=\\frac{K_1x_1^2}{2}\\\\) + \\\\(\\frac{K_2x_2^2}{2}\\\\) Putting the values of \\\\(k_1\\\\),\\\\(k_2\\\\),\\\\(x_1\\\\) and \\\\(x_2\\\\)We get U= 0.4J