Hello!
As it says in the question, a person that is 6 feet tall has a shadow that is 12 feet tall. You would find the length of the shadow of the 33 foot tree by multiplying 33 by 2, since 6 multiplied by 2 is 12, the length of the shadow, then multiplying 33 by 2 will give you a shadow of 66 feet.
So the length of the tree's shadow would be 66 feet tall
I hope this helps!