Solution 1.1:2b

When calculating, the innermost part of the expression should always be calculated first.

\displaystyle 3-((\bbox[#FFEEAA;,1.5pt]{\,(7-4)\,}+6)-5) = 3-((\bbox[#FFEEAA;,1.5pt]{\,3\,}+6)-5).

In the resulting expression we again pick out and calculate the innermost part

\displaystyle \phantom{3-((\bbox[#FFEEAA;,1.5pt]{\,(7-4)\,}+6)-5)}{} = 3-(\firstcbox{#FFEEAA;}{\,(3+6)\,}{9}-5)

\displaystyle \phantom{3-((\bbox[#FFEEAA;,1.5pt]{\,(7-4)\,}+6)-5)}{} = 3-(\secondcbox{#FFEEAA;}{\,(3+6)\,}{9}-5).

Now there is just one bracket to calculate

\displaystyle \phantom{3-((\bbox[#FFEEAA;,1.5pt]{\,(7-4)\,}+6)-5)}{} = 3-\firstcbox{#FFEEAA;}{\,(9-5)\,}{4}

\displaystyle \phantom{3-((\bbox[#FFEEAA;,1.5pt]{\,(7-4)\,}+6)-5)}{} = 3-\secondcbox{#FFEEAA;}{\,(9-5)\,}{4}

and now there is only an expression without brackets left to calculate

\displaystyle \phantom{3-((\firstcbox{#FFEEAA;}{\,(7-4)\,}{3}+6)-5)}{} = -1.