FBX model from Blender doesn't show it's surface in Unity3D

I’ve create a model from Blender and exported it as .FBX file. However when I import this into Unity, the surface is missing.how can i fix?

Screenshot attached:

in Blender it look like this:

in Unity it look like this which only shows it inside:

Looks like the normals are facing the wrong way. Select the faces in Blender and hit CTRL+N to recalculate normals or CTRL+F and select “Flip Normals”.