It is 5 hours:
9pm EST is 2am BST the following day.
24 hours
12 hours.
4to 9pm is how much hours
5 hrs afrter 9am is 2pm; 5 hrs afrter 9pm is 2am
Between 10am and 9pm, there are 11 hours.
There are 17 hours between 9pm and 2pm the following day.
7 hours.
7 hours.
SIX hours !
7 hours
There are 4*(1 + 6*k) hours where k is an integer.