A study of the effects of exercise used rats bred to have high or low capacity for exercise. There were 8 high-capacity and 8 low-capacity rats. The 8 high-capacity rats had mean blood pressure 89 with standard deviation 9, and the 8 low-capacity rats had mean blood pressure 105 with standard deviation 13. In constructing a 95% confidence interval for the difference of the two means (low capacity - high capacity) without additional software, what is the standard error? (Answer to the nearest hundredth.)