A colleague in a foreign country reports that the Young's modulus of a certain layer has been back-calculated from the deformations of a stress increase due to a surcharge, from 20 kPa to 40 kPa. This modulus is given as E = 2000 kPa. A new surcharge is being planned, from 40 kPa to 60 kPa, and your colleague (who is not a geotechnical engineer) asks your advice on the value of E to be used then. What is your suggestion?