Complex sentence: Key also provided illustrations for the long-running "Positive Attitude" series of motivational pamphlets and posters, published biweekly by Economics Press Inc. from the 1960s to the 1980s.
Split into simpler sentences: Key also provided illustrations for the long-running "Positive Attitude" series of motivational pamphlets and posters. The series was published bi-weekly by Economics Press Inc. from the 1960s to the 1980s.