Forget about VM1, If we simplified the circuit and connect two Voltage source of 20 V and 2.5 V, by connecting their GND, over all voltage should be 20V - 2.5V = 17.5 V, now two resistor in series, so over all current trough circuit is, I = V / R. where R = 43 + 5.1 = 48.1 KOhm, and V = 17.5 V so I = 17.5 V / 48.1 KOhm = 0.363825364 mA, Now as you can see, voltage drop across R2 is,

Voltage drop across V_R2 = R2 x I = 1.855509356 V and finally Volt Meter will read value Vm1 = V_R2 + V1 = 2.5 + 1.855509356 = 4.355509356 V

Is that clear?

Forget about VM1, If we simplified the circuit and connect two Voltage source of 20 V and 2.5 V, by connecting their GND, over all voltage should be 20V - 2.5V = 17.5 V, now two resistor in series, so over all current trough circuit is, I = V / R. where R = 43 + 5.1 = 48.1 kOhm, and V = 17.5 V so I = 17.5 V / 48.1 kOhm = 0.363825364 mA, Now as you can see, voltage drop across R2 is,

Voltage drop across V_R2 = R2 x I = 1.855509356 V and finally Volt Meter will read value Vm1 = V_R2 + V1 = 2.5 + 1.855509356 = 4.355509356 V

Is that clear?