Mathematical sentence: \(7\space\text{hours}\space+\space6\space\text{hours}\space-\space4\space\text{hours}\space=\underline{\quad\quad}\,\text{hours}\)
METHOD
\(\begin{array} {rr} \\\space7\;\;\text{hours} \\+\;\;\;\space6\;\;\text{hours} \\\hline\;\;\;1\;3\;\;\text{hours}\\\hline \end{array}\) \(\Longrightarrow\) \(\begin{array} {rr} \\\;1\;3\;\;\text{hours} \\-\;\;\;\space4\;\;\text{hours} \\\hline\;\;\;\;9\;\;\text{hours}\\\hline \end{array}\)
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