(1) error type: difference+error subtraction = minuend 6.9+8.1=15;

Then get the correct difference:15-3.7 =11.3.

(2) Reverse thinking mode: If 3 in the meiotic unit is regarded as 8, it will be reduced by 5, and if 7 in one tenth is regarded as 1, it will be reduced by 0.6.

The correct difference is 6.9+(8-3)-(0.7-0.1) =11.3.