[tex]\displaystyle \\
a) \\ 8\frac{1}{6} : 2 \frac{1}{3}=\frac{49}{6} :\frac{7}{3}= \frac{49}{6} \times \frac{3}{7}=\boxed{\frac{7}{2}} =\boxed{3\frac{1}{2}} =\boxed{3,5} \\ \\
5 \frac{5}{6} : 3 \frac{1}{3} =\frac{355}{6} : \frac{10}{3} =\frac{355}{6} \times \frac{3}{10} =\frac{71}{2} \times \frac{1}{2} =\boxed{\frac{71}{4}}= \boxed{17\frac{3}{4}}=\boxed{17,75} \\ \\ \\
b) \\
( 2,5 + 3 ) ^2 =5,5^2=\boxed{30,25} \\ \\
( 4,5 - 3 )^2 = 1,5^2 = \boxed{2,25}
[/tex]
[tex]\displaystyle \\
c) \\
3\frac{3}{4} - 1,25 = 3,75 - 1,25 = \boxed{2,5} \\ \\
5\frac{1}{4} - 3,75 = 5,25 - 3,75 = \boxed{1,50}[/tex]