Transform (5 square root x^7)^3 into an expression with a rational exponent

I think I understand what you're wanting.  You want to turn that square root problem into one with a fraction as an exponent.  If that's the case, the steps to do that are this:

First start out by simplfiying the square root of
in fraction form pulls the 2, which is called the index over as the denominator in the exponent, with the 7 being the numerator.  So that expression as a square root looks like this as an rational exponent:

But we still have the 5 to content with, so let's add that in there:

not only is the exponent cubed now by multiplication, so is the 5:

The answer would be 13.5 minutes.