To find out how many square feet Christy painted per day, we need to divide the total area painted by the number of days she worked.
Since Christy painted 260 square feet in 3 days, we can calculate the amount she painted per day as follows:
\[ \text{Square feet per day} = \frac{\text{Total square feet}}{\text{Number of days}} = \frac{260 \text{ square feet}}{3 \text{ days}} \approx 86.67 \text{ square feet per day} \]
None of the given options (836, 270, 280, 290) match this approximate value. It appears there may be some confusion with the details, or the numbers provided might not directly lead to a sensible conclusion with the options given.
If you meant to reference a total area that yields one of the choices (like 836 total square feet), then please specify the total area painted, and I can assist in recalculating based on that new context.