Answer
1
Work Step by Step
$-2.1-[2.3-(3.5-(-1.9))]\longrightarrow$ in the innermost parentheses, change subtraction to addition, and reverse the sign of the following term
=$-2.1-[2.3-(3.5+1.9)]\longrightarrow$ add in innermost parentheses
=$-2.1-[2.3-5.4]\longrightarrow$ subtract within brackets
=$-2.1-[-3.1]\longrightarrow$ change subtraction to addition, and reverse the sign of the following term
=$-2.1+3.1\longrightarrow$ add
=$1$
