Question Broken mesh

Hello,
First time posting here so I am sorry if I posted this in the wrong thread.
I'm trying to make a game and did some models in Blender. The problem is when I export the .fbx file to Unity some of the models get broken meshes. The first image is the model in blender, the second is the same model in Unity. What am i doing wrong here?

 

Blender defaults to showing all faces as double sided. Unity's Standard shader, along with most real time shaders, default to single sided. Your mesh's triangles may be partially or entirely inverted. Enable backface culling in Blender's Viewport Shading options and then flip the normal on problematic faces.

 

After using mirroring, always apply scale, then flip normals in Blender. Mirror is a negative scale along one of the axes and it "turns the mesh inside out"

 

That solved it! Thank you so much for the help!