39114

Answer - 20 children, 6 pensioners and 22 adults.

Adults -

£3.50+£3.50=£7.00 *2 adults*
£7.00+£7.00=£14.00 *4 adults*
£14.00+£14.00=£28.00 *8 adults*
£28.00+£28.00=£56.00 *16 adults*
£7.00+£7.00+£7.00=£21.00 *6 adults*
£21.00+£56.00=£77.00 *22 adults*

Children -

£0.85x4=£3.4 *4 children*
£3.4x5=£17.00 *20 children*

£77.00+£17.00=£94.00+£6.00 *For pensioners* = £100!