Hello Jayesh

In the question,  we have

R1 = 3.1 ohm at t = 300C
R2 = 4.5 ohm at t = 1000C


Also We have, R = R0 (1+t)

So, R1 = R0 (1+ * 30)
And,
R2 = R0 (1+ * 100)

Then,
R1 / R2 = [(1+30) / (1+100)]


3.1 /4.5 = [(1+30) / (1+100)]


Solving the above expression we get:


Temp. coefficient, = 0.0085 0C-1


Thankyou