The remainder of his haul have come from his time on Merseyside and a loan spell at West Bromwich Albion.
"It's not bad. But I want to add trophies to the personal stuff. There's a lot of hard work to be done and I'm enjoying the challenge," Lukaku told the club's website (http://www.manutd.com).
Lukaku's goal before an Alexis Sanchez strike on Saturday helped United remain on course to finish second in the league behind runaway leaders Manchester City. Jose Mourinho's side have 68 points with seven games remaining in the season.
United's only realistic chance of silverware this season lies in the FA Cup, where they take on an in-form Tottenham Hotspur side in the semi-finals later this month.
"I don't like to talk about personal stuff," Lukaku added. "I'm a team player so I put the team ahead of myself. I'm a striker and I know there are a lot more goals in me, and hopefully I can add a trophy as well to the goals."
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Toby Davis)
