Measure 9 minutes from 2 hourglasses puzzle

Using only a Four-minute hourglass and a seven-minute hourglass,
How will you measure exactly nine minutes?

Restriction:- Without the process taking longer than nine minutes.

Answer:-

We measure 7 Minute from One Hourglass. We reverse it at 7th minute.
And, 4+4=8 Minutes from Second Hourglass:- 8 Minutes
8(from 1)-7(From 2) = 1 Minute  :-1 Minutes, Hence total is-
TOTAL = 9 MINUTES

EXPLANATION-

0 Minutes – Start both hourglass at the same time.
4 Minutes – The four minute glass runs out. Flip the four minute glass.
7 Minutes – The seven minute glass runs out. Flip the seven minute glass.
8 Minutes – The four minute glass runs out; the seven minute glass has been running for one minute. Flip the seven minute glass.
9 Minutes – The seven minute glass runs out.