Answer
The treasure must be buried under the flagpole.
Work Step by Step
a. If this house is next to a lake, then the treasure is not in
the kitchen.
b. If the tree in the front yard is an elm, then the treasure is
in the kitchen.
c. This house is next to a lake.
d. The tree in the front yard is an elm or the treasure is
buried under the flagpole.
e. If the tree in the backyard is an oak, then the treasure is
in the garage.
c ∧ a → The treasure is not in the kitchen [Modus Ponens]. .....(p)
p ∧ b → The tree in the front yard is not an elm[Moodus Tollens] .....(q)
q ∧ d → The treasure is buried under the flagpole[Elimination] which is our answer
