1.) The length-weight relationship for the pacific Halibut can be approximated by the function L(w)=.46*cube-root(w), where w is the weight in kilograms and L is the length in meters. If the halibut's weight is 230 kilograms, what is its length?

Okay seems simple enough and I set it up like this:

L(w)=.46*cube-root(260)

Well, if you cube both sides you end up with 25.30736 but with a cube on the other side. It puts you back in the same spot. Any ideas?

2.) A truck on the highway is traveling at 55 mph. Three hours later, a car gets on the same highway at the same place as the truck and begins traveling in the same direction at 75 mph. After what distance will the car overtake the truck?

I don't know how to set this equation up.

3.) It takes a boy 90 minutes to mow the lawn, but his sister can mow it in 60 minutes. How long would it take them to mow the lawn if they worked together using two lawn mowers?

Here is how I set this up:

1/90+1/60=1/t and solved for t, which gave me 25.7 minutes. Does that seem right?