Complex sentence: In 1969, Serota became Chairman of the new Young Friends of the Tate organisation with a membership of 750 in a building in Pear Place, south of Waterloo Bridge, arranging lectures and Saturday painting classes for local children.
Split into simpler sentences: In 1969, Serota became Chairman of the new Young Friends of the Tate organisation with a membership of 750. They took over a building in Pear Place, south of Waterloo Bridge, arranging lectures and Saturday painting classes for local children.