(((0.5*4200*(100-7))/0.8)/(3.6*(10^6)))*4

((((0.5*4200*(100-7))/0.8)/60)/230)

(((0.5*4200*(100-7))/0.8)/20)(1/(60*60))

res=T[x]/.DSolve[{λ*D[D[T[x],x],x]==0,T[0]==T1,T[d]==T2},T[x],x][[1]]

Plot[Evaluate[res/.{d->0.5,λ->0.4,T1->40,T2->20}],{x,0,0.5}]

rovnice={λ*D[D[T[x,t],x],x]==ρ*Cp*D[T[x,t],t],T[0,t]==20+20((Tanh[100(t-1)]+1)/2),T[d,t]==T2,T[x,0]==T2}/.{d->0.5,λ->0.4,T1->40,T2->20,ρ->2000,Cp->400}
res2=NDSolve[rovnice,T[x,t],{x,0,0.5},{t,0,60*60}][[1]]

{0.4` Derivative[2,0][T][x,t]==800000 Derivative[0,1][T][x,t],T[0,t]==20+10 (Tanh[100 (0+t)]),T[0.5`,t]==20,T[x,0]==20}

Plot[20+20((Tanh[100(x-1)]+1)/2),{x,-5,5}]