What is 7+3?

A policeman was patrolling a local parking spot overlooking a golf course. He drove by a car and saw a couple inside with the dome light on. There was a young man in the driver's seat reading a computer magazine and a young lady in the back seat knitting. He stopped to investigate.
He walked up to the driver's window and knocked. The young man looked up, cranked the window down, and said, "Yes, officer?"
"What are you doing?" the policeman asked.
"What does it look like?" answered the young man. "I'm reading a magazine."
Pointing towards the young lady in the back seat, the officer then asked, "And what is she doing?"
The young man looked over his shoulder and replied, "What does it look like? She's knitting."
"And how old are you?" the officer then asked the young man.
"I'm nineteen," he replied.
"And how old is she?" asked the officer.
The young man looked at his watch and said, "Well, in about twelve minutes she'll be eighteen."