octave:12> R=[68; 120; 150]
R =
    68
   120
   150
octave:13> T=[20; 100; 227]+273.15
T =
   293.15
   373.15
   500.15
octave:14> A=[ones(3,1), log(R), (log(R)).^3]
A =
     1.0000     4.2195    75.1252
     1.0000     4.7875   109.7297
     1.0000     5.0106   125.7993
octave:15> coeff=A\(T.^(-1))
coeff =
  -2.0064e-02
   8.3923e-03
  -1.5888e-04
octave:16>
octave:16> x=68; 1/(coeff(1) + coeff(2) * log(x) + coeff(3) * log(x).^3)
ans =  293.15
octave:17> x=120; 1/(coeff(1) + coeff(2) * log(x) + coeff(3) * log(x).^3)
ans =  373.15
octave:18> x=150; 1/(coeff(1) + coeff(2) * log(x) + coeff(3) * log(x).^3)
ans =  500.15