m=3;
c=4180;
deltaT=70;
teplo=m*c*deltaT

5*877.800/3600

lambda=0.7;
res=DSolve[{lambda*D[D[T[x],x],x]==0,T[0]==20,T[0.6]==4},T[x],x]

Plot[T[x]/.res,{x,0,0.8}]