@Earl 

plot3d([100*(.15+0.35e-1*x)+100*(y+0.35e-1*(9-3,8*(1+y)))+,6*(100*(-.15-.35*x)*x ], x = 2 .. 9, y = .1 .. .45, axes = boxed);

Thank you for your quick response.
In the next task I am again facing the same problem, could you explain to me what error I am doing?