\(a,2^{18}=2^3.2^{15}=8.2^{15}.\\ \Rightarrow7.2^{15}< 8.2^{15}.\\ \Rightarrow7.2^{15}< 2^{18}.\)
\(b,27^5=3^{15}.\\ 243^3=3^{15}.\\ \Rightarrow27^5=243^3.\)
\(c,3^{200}=9^{100}.\\ 2^{300}=8^{100}.\\ \Rightarrow9^{100}>8^{100}.\\ \Rightarrow3^{200}>2^{300}.\\ \)
\(d,8^{30}=2^{90}.\\ 2^{91}>2^{90}.\\ \Rightarrow2^{91}>8^{30}.\)


