It's hard to say anything without knowing the precise data or what kind of interpolation you want. If you want to do a linear interpolation, the simplest kind, then you would use a formula like where is the temperature, listed in the table, just less than the temperature you are given, is the pressure, listed in the table, just higher than the pressure you are given, and is the enthalpy given by the table at and . You can then determine the two coefficients, a and b, by using the temperature and pressure just above the temperature and pressure you are given to get two linear equations to solve for a and b. Once you have found a and b, put the temperature and pressure you are given into to find the (interpolated) value of K.
(Actually, you could use any two of , or where and are the temperature and pressure given in the table just above the temperature and pressure you are given. If the formula were really linear, those would all give the same result but are more likely to get 3 slightly different results. There is no "correct" answer here- interpolation is an approximation.