How did Rock and Roll grow and change throughout the 50's and 60's?

At the height of the initial pandemonium, in 1955-56, a select number of front-runners emerged, stars whose personalities and performing antics set the stage for all that was to follow: Elvis, of course; Chuck Berry, whose definitive guitar style (rooted in swing jazz and the uptown band blues of T-Bone Walker) was as widely emulated as his brilliant, vividly economical lyrics of teenage tribulations and triumphs.

answer:   2 1/4 pounds

explanation: 4 1/2 - 2 3/4