the total voltage across the end points is 5 V
so, Vtotal = V(thermistor) + V(resistor)
5= 2 +Vr
Vr= 3 Volt
the current passing through the Resistor I= V/ R
so I = 3/1050
I=1/350 A
while the Resistor and thermistor are series the I(total) = I(thermistor) = I(resistor) = 1/350 A
Voltage at the thermistor = 2V
so r = V/ I
then R(thermistor) = 700 ohm