Issue to build and run app in Xamarin Form Application with Visual Studio 2017

Hi,

I am Developing Android Application in Visual Studio 2017. When Bulid and run this project it is giving a error.

The $(TargetFrameworkVersion) for Xamarin.Forms.Platform.Android.dll (vv8.0) is greater than the $(TargetFrameworkVersion) for your project (v7.1). You need to increase the $(TargetFrameworkVersion) for your project.

Please Resolve this issue