How long does it take light to travel

[ducmod]

Homework Statement

Hello!
This is an elementary problem, but I somehow can't compute it.

How long does it take light to travel in:
(a) 1.0 ft (report answer in nanoseconds)

(b) 4.5 billion km, the average separation between
the sun and Neptune (report answer in hours
and minutes)

Here is what I have tried:
(a) I assume 1.0ft means 1 foot. Light travels 3 x 10^8 meters / second, or 186 000 miles per second (information from a chemistry textbook). 1 meter = 3.2808 feet, hence
9.8424 x 10^8 feet in 1 second
1 foot in x seconds
hence it takes 1 / (9.8424 x 10^8) = 0.10168 x 10^(-8) seconds
To transfer to nanoseconds, I need to divide by 10^(-9), and I get 0.10168 x 10^(-8) / 10^(-9), hence
I get 1 nanosecond as the answer. Correct?

(b) 3 x 10^8 meters / second, hence 0.003 x 10^8 km/ second,
4.5 x 10^8 km / 0.003 x 10^8 km = 1500 seconds
There are 3600 seconds in one hour, hence 3600 / 1500 = 2.4 hours.
This answer is wrong, it should be 4 hours 10 minutes

Thank you!

 

[Borek]

I get 1 nanosecond as the answer.

Yep, 1 ft/ns, strange, but quite useful sometimes.

4.5 x 10^8 km

First mistake.

There are 3600 seconds in one hour, hence 3600 / 1500

Second mistake.

 

[ducmod]

Yep, 1 ft/ns, strange, but quite useful sometimes.
First mistake.
Second mistake.

Thank you, but what are my mistakes?

 

[Borek]

Come on, I told you were they are, do some effort and rethink your numbers and what you did with them. You will learn much more if you find what is wrong on your own than if I spoon feed you what the problem is.

 

[Borek]

Sigh, there goes my pedagogy.

 

[SteamKing]

Sigh, there goes my pedagogy.

I deleted my post Borek. I didn't see your Post #4.