https://support.google.com/edu/classroom/thread/326745621?hl=en&sjid=11921282876252340916-NA

https://superuser.com/questions/1882251/faqs-solve-what-does-non-refundable-mean-on-expedia

https://superuser.com/questions/1882250/customer-helpus-is-expedia-non-refundable

https://philpeople.org/profiles/does-frontier-offer-fully-refundable-tickets-4

https://philpeople.org/profiles/does-frontier-offer-fully-refundable-tickets-5

https://philpeople.org/profiles/does-frontier-offer-fully-refundable-tickets-8

https://philpeople.org/profiles/does-frontier-offer-fully-refundable-tickets-6

https://philpeople.org/profiles/does-frontier-offer-fully-refundable-tickets-7

https://www.goodreads.com/topic/show/23045021-tuesday-mania-offer-what-is-the-cheapest-day-to-book-a-flight-on-delta

https://www.goodreads.com/topic/show/23045016-what-day-is-american-airlines-cheapest-to-buy-tuesday-faqs