Complex sentence: Throughout the 1930s Armstrong continued to work as a designer as he also continued to develop his art. He produced a number of remarkable posters for Shell and also produced a 1935 poster for the Royal Mail.
Split into simpler sentences: Throughout the 1930s Armstrong continued to work as a designer as he also continued to develop his art. He produced a number of remarkable posters for Shell. Armstrong also produced a 1935 poster for the Royal Mail.