If we multiply cbrt(a) on both the denominator and numerator, we get (a*sqrt(a)*cbrt(a))/a. The a's cancel out and we are left with sqrt(a)*cbrt(a) = a^k. sqrt(a) can also be written as a^(1/2) and cbrt(a) can be written as a^(1/3). Because they are multiplying each other, we add the exponent to get k = 5/6