Scalar subqueries Question 3

Screen Link:

My Code:

SELECT first_name || last_name AS name, (SELECT SUM(total)
                                FROM invoice
                               WHERE customer_id = 18) AS total
  FROM customer
 WHERE customer.customer_id = 18

What I expected to happen:

What actually happened:

Something is wrong with the subquery.

The subquery returned the wrong value. 
It should have returned Michelle Brooks, but it returned 79.2 instead.

Not sure where I am making the mistake here. My output is correct
because I am getting one name and one number