A 15 foot flagpole casts an 11 foot shadow. At the exact same time a 28 foot tree casts a shadow. Which proportion would correctly find the length of the tree's shadow?

We have to set up consistent ratios to make the proportion, for example, shadow length divided by actual object height.
For the flagpole: 11/15For the tree: x/28
Equating these gives:

(11)/(15)=(x)/(28)