Answer:
by choosing to end the sentence in a preposition
Step-by-step explanation:
Formal language can be seen with the use of "on which", changing the position of preposition "on" by moving it to the end of the sentence with the relative pronoun "which" omitted changes it to informal English.
"Mr. Richardson is shopping for the perfect shelf on which to display his bowling trophy."
would change to
"Mr. Richardson is shopping for the perfect shelf to display his bowling trophy on."