Convert the 5th root of x^3 into a rational expression and explain the steps

What is the radius of a circle with an area of 78.5 cubic inches? use 3.14 for pie

The serenity and the mystic are sail boats. the serenity and the mystic start at the same point and travel away from each other in opposite directions. the serenity travels at 16 mph and the mystic travels at 19 mph. how far apart will they be in 3 hours?

What is the solution for 6 - 7/8? explain the steps.