You only need to know pressure altitude and then multiply by Mach Number to get the flight EAS.
Values:
Press.Alt Speed of sound
65000 ft - 156.02 kts EAS
70000 ft - 138.35 kts EAS
75000 ft - 122.69 kts EAS
80000 ft - 108.8 kts EAS
I'm probably being a bit thick this morning, but it looks like you have missed something out.
If I am reading you correctly you are saying that the EAS in the right hand column is the local speed of sound (Mach 1) at the pressure altitude in the left hand column.
How do we get from the pressure altitudes that you have quoted, to the EAS values by multiplying by Mach 1?