The correct answer is - One parent has white feathers and one has red/white feathers.
The offspring, the chickens, have feathers that are only white, or feathers that are with both red and white color. There's not a single individual in the offspring that has only red feathers.
That leads to the conclusion that one of the parents had white feathers, while the other had red and white feathers, as those are the only two combinations in their offspring.
A parent that has only red feathers can be excluded (though not 100%) because there's not a single chick out of the 30 chicks with red feathers, and if there was a red feathered parent the chances are very high that at least one of them will be red feathered as well.