Multiple conditiions on data table HELP!!

Hi,

See attached document, would really appreciate some help on this one, way out of my comfort zone!

O.K so based on the array type, temperature, FEQ hours and ground conductivity, i need to match the result to the table data. If there is no exact match I would need the next lowest data as opposed to higher.

Ideally I would like to be able to formulate the result by some clever maths using the data from the above and below and dividing it by the difference, but I think that may be asking to much???!!!

However, I would greatly appreciate anyones help overcoming this formula.

Thanks in advance!

Sam