A
[tex] \frac{ {5}^{3} }{ {5}^{6} } = {5}^{ - 3} [/tex]
B
[tex]( {14}^{3} ) {}^{6} = {14}^{18} [/tex]
C
[tex] {8}^{3} \times {8}^{6} = {8}^{9} [/tex]
D
[tex] \frac{ {16}^{6} }{ {16}^{3} } = {16}^{3} [/tex]
E
[tex]( {21}^{3} ) {}^{ - 6} = {21}^{ - 18} [/tex]
hope this helps
good luck