Complex sentence: In 1941 his work was exhibited at the Royal Hibernian Academy for the first time and between 1941 and 1971 he exhibited every year (but for three occasions) at the RHA cumulatively showing in the region of one hundred paintings.
Split into simpler sentences: In 1941 his work was exhibited at the Royal Hibernian Academy for the first time. Between 1941 and 1971 he exhibited every year (but for three occasions) at the RHA cumulatively showing in the region of one hundred paintings.