Electrical Engineering Prelab - Absolute value of gate voltage
That's not a minus sign. It's a dash. It's saying the thermistor has a range from 50 K to 30K (and, apparently, a negative temperature coefficient). 

So, your task is to compute the gate voltage when the thermistor is at 50K, and again when it's at 30K.

Since you just want to compute the gate voltage, look only at the left block of your schematic. What sort of circuit does that look like on its own? I.e., given something like this:







simulate this circuit &ndash; Schematic created using CircuitLab

What voltage do you get at Vout based on V1, R1, and R2?