I think that the answer is obvious.
A banana tree can grow up to 20 to 30 feet tall.
A lemon tree typically grows to be around 10 to 20 feet tall.
An orange tree typically grows to be around 20 to 30 feet tall and 15 to 20 feet wide.
The ratios are in the same proportion, so all you need to really figure out is what is in the same ratio to 20 as 6 is to 4.
A magnolia tree typically grows to be around 20 to 80 feet tall, depending on the species.
A cherry tree can grow up to 30 to 40 feet tall and have a spread of 20 to 30 feet wide.
Assuming the shadows are measured at the same time of day and that the trees are on level ground, the tree with a 20-foot shadow is a quarter longer than the tree with a 16-foot shadow. Adding a quarter of the height to 12 feet makes it 15 feet tall. Alternatively use the tangent ratio which will be opposite (height of 1st tree) over adjacent (its shadow) and multiply it by the adjacent of the 2nd tree: (12/16)*20 = 15 feet tall.
A cherry tree typically grows to a height of about 20 to 30 feet.
A plum tree typically grows to a height of 15 to 20 feet.
An olive tree typically grows to a height of 20 to 40 feet.
ABOUT 2O FEET
A cherry tree typically grows to be about 20 to 30 feet tall and 15 to 25 feet wide.