Essential algebra / C.L. Johnston, Alden T. Willis, Jeanne Lazaris. - 5th ed. - Belmont, Calif. : Wadsworth Pub. Co., c1988. - xiv, 683 p. : ill. ; 28 cm. - The Johnston/Willis developmental mathematics series . - Johnston, C. L. 1911- (Carol Lee), Johnston/Willis developmental mathematics series. .