2. The original formula = | 6+(-12) || 3-(-15) | = | 6-12 ||| 3-(-15) | = | 6-/kloc.
Solve this kind of problem: 1. The brackets are preceded by a-sign, and the number should be changed if the brackets are removed [example: -(-3)=+3], and the brackets are preceded by a+sign, and the brackets are not changed [example: +(-3)=-3].
2. If there is an absolute value calculation, first calculate the value in the absolute value according to the above method, then change the calculated value to a positive value and remove the absolute value symbol.