I have 4 points that each are 64 x,y values apart with different Z values that are arranged like this with 90 degree angles:

0,0 64,0

0,64 64,64

Also inside that square there is a 5th value I only have the X and Y value of and need to find the Z value of.

If anyone has any ideas on how to solve this id greatly appreciate it I have been at this for hours...