Sean has worked 66 hours over the last 10 days without a day off. He worked either a 6 hour day or an 8 hour day. During the 10 day period, how many days did Sean work an 8 hour day?

He worked an 8 hour day 3 days.

Let x be the number of 8 hour days he works. Then 10-x is the number of 6 hour days he works.

8x + 6 (10-x) = 66

Using the distributive property,

8x + 6*10 - 6*x = 66

8x + 60 - 6x = 66

Combining like terms,

2x + 60 = 66

Subtract 60 from both sides:

2x + 60 - 60 = 66 - 60

2x = 6

Divide both sides by 2:

2x/2 = 6/2

x = 3

There were 3 days he worked 8 hours.