Q=((1*4200*(100-10))/0.7)

((Q*4)/(3.6*(10^6)))

(9000/231.)

λ=0.3;
d=1;

res=T[x]/.DSolve[{λ*D[D[T[x],x],x]==0,T[0]==40,T[d]==10},T[x],x][[1]];

Plot[res,{x,0,d}]

ρ=2000;
Cp=500;
res2=T[x,t]/.NDSolve[{λ*D[D[T[x,t],x],x]==ρ*Cp*D[T[x,t],t],T[0,t]==10+30((Tanh[100(t-3)]+1)/2),T[d,t]==10,T[x,0]==10},T[x,t],{x,0,d},{t,0,10*24*60*60}][[1]]

Plot[10+30((Tanh[100(x-1)]+1)/2),{x,-5,5}]

Plot3D[res2,{x,0,d},{t,0,2*24*60*60},PlotRange->All]

Plot[res2/.t->10*24*60*60,{x,0,d}]