In this question, the oil production at 2004 (which was 731000barrel/day) was reduced at 2005(into 537500 barrel/day). You are asked the percentage reduction. To answer this, you need to determine how much the decrease in barrel/day then divide it by the initial production before reduced(production at 2004)
The reduction would be: 731,000 barrels/day - 537,500 barrels/day = 193,500 barrels/day
Then divide it with initial production: (193,500barrels/day )/(731,000 barrels/day) * 100% = 26.47%
