An Artist Intends to Paint a 70-Square-Foot Mural on a Wall

Short Answer

An artist intends to paint a 70-square-foot mural on a wall that is 20 feet long and 11 feet high. If the artist wants to leave a border of uniform width, how wide should the border be?
( Hint: Let $w$ represent the width of the border. Then $20 - 2 w$ represents the length of the mural.)
__________ ft