Unanle to use MVC6 grid inside my asp.net mvc core. Error "'IHtmlHelper' does not contain a definition for 'Grid' ...

I want to use MVC6 grid from this link https://mvc6-grid.azurewebsites.net/ so i install the

Install-Package NonFactors.Grid.Mvc6

but inside my view when i write the following :-

@model IEnumerable<LandingPageFinal3.Models.Doctor>
@(Html
.Grid(Model)
.Build(columns =>
{
    columns.Add(model => model.Name).Titled("Name");
    columns.Add(model => model.Surname).Titled("Surname");

    columns.Add(model => model.Age).Titled("Age");
    columns.Add(model => model.Birthday).Titled("Birth date");
    columns.Add(model => model.IsWorking).Titled("Employed");

//popup part
columns.Add(model => $"<a  data-modal='' data-id=\"{model.Id}\"     href='PasswordRestUser/{model.Id}'      id=\"ss\"  asp-    action=\"PR\" asp-route-id=\"@item.Id\" class=\"btn     btn-info\" '> PR <span class='glyphicon      glyphicon-user'> </span> </a>").Encoded(false);

})
.Filterable()
.Sortable()
.Pageable()
)

<div id='myModal' class='modal fade in'><div class="modal-dialog"><div class="modal-content"><div id='myModalContent'></div></div></div></div>

i got this error:-

Severity	Code	Description	Project	File	Line	Suppression State
Error	CS1061	'IHtmlHelper<IEnumerable<Doctor>>' does not contain a definition for 'Grid' and no accessible extension method 'Grid' accepting a first argument of type 'IHtmlHelper<IEnumerable<Doctor>>' could be found (are you missing a using directive or an assembly reference?)	

any advice on this?