$\text{a)}$  

$x=\frac{27}{72}=\frac{27:9}{72:9}=\frac{3}{8}$  

$y=\frac{36}{96}=\frac{36:6}{96:6}=\frac{6}{16}=\frac{6:2}{16:2}=\frac{3}{8}$  

$x=y$        

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$\text{b)}$  

$x=\frac{60}{108}=\frac{60:2}{108:2}=\frac{30}{54}=\frac{30:6}{54:6}=\frac{5}{9}$  

$y=\frac{75}{135}=\frac{75:5}{135:5}=\frac{15}{27}=\frac{5}{9}$  

$x=y$  

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$\text{c)}$  

$x=\frac{84}{156}=\frac{84:2}{156:2}=\frac{42}{78}=\frac{42:6}{78:6}=\frac{7}{13}$  

$y=\frac{126}{246}=\frac{126:2}{246:2}=$   $\frac{63}{123}=\frac{63:3}{123:3}=$   $\frac{21}{41}$  

$x\ne y$