Q:

            We need to calculate the value of VR₃ where values of VR₁ and VR₂ are known by using KVL.

Solution:

            We will take increase in energy level as positive & decrease in energy level as negative. By considering this assumption and KVL the equation of this loop will

                                     +VR₁ - 5 + VR₂ - 15- 30 +VR₃ =0

            That can be written like

                                 +VR₃ +VR₂ +VR₁= 30 +15 +5= 50

            Now imagine that VR₁ & VR₂ are known to be 18Volt and 12Volt respectively then             

                                                            VR₃=20 Volts              Ans.