How do you find out how many times does 7 appear on a digital clock in 24 hours?

There are four digits on a digital clock. A seven will never appear in two of them.

It will appear 6 times per hour (07, 17, 27, 37, 47, 57) and once each at 7 am and 7 pm, or 700 and 1700 if you're keeping military time. My best guess: 24 x 6 + 2 = 144