Final answer:
Britney watched TV for 2/3 hour.
Step-by-step explanation:
To find out how long Britney watched TV, we need to find 4/5 of the time she practiced piano for. Britney practiced piano for 10/12 hour, which is equivalent to 5/6 hour. To find 4/5 of 5/6 hour, we multiply 5/6 by 4/5.
5/6 * 4/5 = 20/30 = 2/3
So, Britney watched TV for 2/3 hour, which is equivalent to option b.
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