Which expression is equivalent to startfraction (5 a b) cubed over 30 a superscript negative 6 baseline b superscript negative 7 baseline endfraction? assume a not-equals 0, b not-equals 0. startfraction a superscript 7 baseline b superscript 10 baseline over 6 endfraction startfraction 125 a superscript 18 baseline b superscript 21 baseline over 30 endfraction startfraction 25 a cubed b superscript 4 baseline over 6 endfraction startfraction 25 a superscript 9 baseline b superscript 10 baseline over 6 endfraction