The 3 unknown calculator requires input to be in the form:
     aX  +   bY   +   cZ   =   d
EXAMPLE:  If you have the equations:
2X   +  3Y   +     4Z   =  119 
5X     - 6Y   +     7Z   =    80 
8X   +  9Y   +   10Z   =  353 
Then your input would be:
Eqtn 1:     2         3        4       119                
Eqtn 2:     5       - 6        7         80                
Eqtn 3:     8         9       10      353                
Click E N T E R and your answers should be:
X=12   Y=13   Z=14