How Did L.A. Rams Calculate What to Offer in Blockbuster NFL Draft Trade?

The Los Angeles Rams shocked the football world yesterday with a dramatic trade with the Tennessee Titans allowing them to secure the first pick in the April 28th NFL Draft. They are positioned to enhance their team by selecting a potential franchise quarterback. The Rams have also sent a signal to Southern California and their newfound fans that they are serious about winning and fielding an interesting team. Pairing a newly drafted quarterback with Pro Bowl Running Back Todd Gurley is the type of star combination that Los Angeles gets excited about. How did the team calculate what was the right combination of draft picks to offer to move from the 15th position to number one? And what criteria do other teams use to calculate draft trades and their value?