Olivia needs to determine the approximate height of a tree in her yard. She measures the length of the shadow of the tree to be 20 ft. At the same time, standing beside the tree, her shadow is 10.5 ft long, and her height is 5 ft 4 in. Approximately how tall is the tree?

a. 10.25 ft
b. 8.75 ft
c. 12.50 ft
d. 15.75 ft