in the first case:
[tex]\begin{gathered} a)7(9+\frac{4}{5})\longleftarrow\text{ in this case is better to compute the parenthesis first.} \\ b)6+8+(2\frac{4}{7})(9)\longleftarrow in\text{ this case, we must convert the mixed fraction first } \\ c)8(\frac{7}{11}+0.1687)\longleftarrow\text{ in this case is better to convert fraction into decimals} \\ d)6(5^2+3^2)\longleftarrow inthiscase,wemustfind5^2and3^2 \end{gathered}[/tex]In tha last case,
[tex]\begin{gathered} i)\text{ 5+6+9 }\longleftarrow\text{ the order of the adittion doenst matter} \\ ii)\text{ (5}\cdot6)\cdot(7\cdot5)\longleftarrow\text{ the order of the product doenst matter} \\ ii)\frac{5\cdot6}{6\cdot7}\longleftarrow\text{ we can compute the product first or we can divide first} \end{gathered}[/tex]