How do I get the path og the images/files that I from Ids ?

@foreach (var item in galleryCollection) {
var imgArr = item.billeder.ToString().Split(new string[] { "," }, StringSplitOptions.None);

    <p>@item.Name</p>
    <p>@item.argang</p>

        foreach(var imgId in imgArr){

            <p> @imgId <br></p>

        }
}

I have tried something like this – which I've been lucky with before:

var Img =  Library.MediaById(imgId.Image);
var ImgPath = Umbraco.Media(imgId).Url;

But it gives me an error:

Compilation Error Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. Compiler Error Message: CS0103: The name 'Library' does not exist in the current context

Source Error:

Line 146:   foreach(var imgId in imgArr){
Line 147:                                           
Line 148:   var Img =  Library.MediaById(imgId.Image);
Line 149:   var ImgPath = Umbraco.Media(imgId).Url;
Line 150: