Assume h_FE3 = h_FE4 = 100. This means that the total h_FE of each darlington is 2000. I_RL,max = 1.4A => I_E1,max = 1.4A. I_B1,max = I_E1,max/(h_FE+1) = 1.4A/2001 = 0.7mA = I_R1. V_B1,max = 11.3 + 2∙0.7 = 12.7V => V_R1 = VS - V_B1 = 15 - 12.7 = 2.3V. R1 = V_R1/I_R1 = 2.3V/0.7mA = 3.3kΩ.

Let's now calculate the maximum power dissipation in T1 and T2. P_T1 = V_CE1∙I_E1 = (VS - V_RL)∙(V_RL/RL) = (VS∙V_RL - V²_RL)/RL. P_T1 reaches its maximum value if dP_T1/dV_RL = VS - 2∙V_RL = 0 => V_RL = VS/2 = 7.5V. P_T1,max = (15∙7.5 - 7.5²)/8 = 7W. Since T1 works only during the positive half periods, T1's (and T2's) maximum dissipation will be 3.5W.