The number of hours she practices each day is unknown, so let's call it x.
She practices dancing x hours each day she goes to practice.
Since she practices 3 days per week, in a week she practices 3x hours.
In two weeks she practices 2(3x) hours, or 6x hours.
We are told she practices 12 hours in 2 weeks, so 6x must equal 12.
The equation is
6x = 12
We can solve it by dividing both sides by 6.
x = 2
She practices 2 hours per day.
Check:
2 hours per for 3 days = 2 * 3 hours = 6 hours in 1 week.
In 2 weeks, she practices 2 * 6 hours = 12 hours.
Our solution is correct.