Answer:
2.5%
Step-by-step explanation:
We start at 2.6. This is an increase of 0.5%.
The increase goes up 1% every 0.4 points. This means the next increase is at 2.6+0.4 = 3.0; this is an increase of 0.5+1 = 1.5%.
The next increase is at 3.0+0.4 = 3.4; this is an increase of 1.5+1 = 2.5%.