6) Найдем наработку на отказ элемента 1:

$$T_{H1} = \frac{1}{\Lambda_4 \rho_1 \rho_2 \rho_3} (1 + \rho_1 + \rho_2 + \rho_3) = \frac{M_1M_2M_3 + M_2M_3\Lambda_1 + M_1M_3\Lambda_2 + M_1M_2\Lambda_3}{\Lambda_4\Lambda_3\Lambda_2\Lambda_1} = \frac{\mu_1^3 + 6\lambda\mu_1^2 + 5\lambda\mu_1^2 + 4\lambda\mu_1^2}{\frac{360 \lambda_1^4}{360 \lambda_1^4}} = \frac{\mu_1^3 + 15 \mu_1^2 \lambda_1}{360 \lambda_1^4}$$ где $$\rho_i = \frac{\Lambda_i}{M_i}$$