(((110^2)-(100^2))/(10*10))

ρ=1500;
Cp=3500;
λ=10;
tloustka=0.05;
res=NDSolve[{ρ*Cp*D[T[x,t],t]==λ*D[T[x,t],{x,2}],T[x,0]==7,-λ*D[T[tloustka,t],x]==10*10*(T[tloustka,t]-7),-λ*D[T[0,t],x]==10*10*(200-T[0,t])},T[x,t],{x,0,tloustka},{t,0,500}]

Plot3D[Evaluate[T[x,t]/.res],{t,0,300},{x,0,tloustka}]

tepl=T[x,t]/.res;

tepl/.{x->0.02,t->400}

116

(0.01/0.025)0.5