Rate of Income pushes through lower business taxes, adding 25% to what reaches your train hideout vault. It needs Shell Company.
Rate of Income is entry 8 of 13 in the Swindler branch, one of the three branches (Ringleader, Insider and Swindler) on the Rooks' 39-upgrade board. It is bought with money and materials, not skill points: £8,000, 25 Silk, 25 Chemicals. Before Rate of Income unlocks you need Shell Company.