A study was conducted to test the effectiveness of a juggling class. Before the class started, six subjects juggled as many balls as they could at once. After the class, the same six subjects juggled as many balls as they could. The differences in the number of balls are calculated. The differences have a normal distribution. Test at the 1% significance level. (Calculate "after" - "before.")
Subject ABCDEF
Before 343245
After 456456
What is the sample mean difference? (Round your answer to two decimal places.)