Example 9.7-1 Error in Thermocouple Measurement

>  restart;
>  T1:=500*F; Tw:=350*F; h:=120*Btu/(hr*ft^2*F); 
k:=60*Btu/(hr*ft*F);B:=0.08*inch; L:=0.2*ft;
>  N:=sqrt(h*L^2/(k*B));  eq. 9.7-8
>  inch:=ft/12.;
>  N;
>  eq:=(T1-Ta)/(Tw-Ta)=cosh(0)/cosh(N);
>  solve(eq,Ta);The text reproted 510F