$$\left. \begin{array} { l } { 9 + 2.5 \div 0.5 - 1 \quad 1.2 } \\ { 9 + 2.5 \div 0.5 - 1 \quad 1.2 } \\ { 8.5 + 1.7 + 1.2 } \\ { ( 8.5 + 1.7 + 1.2 ) - 1.2 } \end{array} \right.$$
