a. The tree is 30 feet tall.
b. The tree is 24 feet taller than Frank.
Since the shadow of the tree is 20 feet and the shadow of Frank is 4 feet, 20+4 is 24. 24+6 is 30, so the tree is 30 feet tall and the tree is 24 feet taller than Frank.
16 is how much taller the tree is then frank