3x+5y+7z= 1 1 b

4x-y+2z=- 1 degree Celsius

From a, x=y+z- 1, d, replace b and c, 3 (y+z-1)+5y+7z =1/e is 8y+10z-66.

4 (y+z-1)-y+2z =-1f is 3y+2z-3=0 h, which becomes a binary linear equation. Just solve g and h at the same time. Multiply g-5 by h, eliminate the unknown z and y, and then substitute g and z to get it.