parameter table:

$\backslash$table$[[,,$Destination,Supply$],[,,1,2,3,4,5],[$So irce,$1,8.,6,3,7,5,20],[2,5,M,8,4,7,30],[3,6,3,9,6,8,30],[$A$($D$),0,-0,0,0,0,20],[$De:riand,$25,25,20,10,20,]]$

After several iterations of the transportation simplex method, a BF solution is obtained that has the following basic variables: $x_{13}=20,x_{21}=25,x_{24}=5,x_{32}=25,x_{34}=5,x_{42}=0,x_{43}=0,x_{45}=20.$ Continue the transportation simplex method for two more iterations by hand. After these two iterations, state whether the solution is optimal and, if so$,$ why.