Display a query result in a textbox?

I know in a combo box you can use the record source to call a table/query and have data displayed in the combo box.

What about in a textbox? I have a form which is already referencing a query.

Now, I created a query which gets certain equipment records from an account and sums them up.

I ran the query and it works fine.

However, how do I display this sum in the textbox on the form?

I tried adding this query to the query that is being used by the form, than i set the control source for the textbox to the sum, but it still won't show.