Hamburger sells 3 pounds for six dollars if samantha 510 pounds of hamburger how much will she pay

I believe you meant to say that if Samantha bought 510 pounds of hamburger, how much will she pay?
 
Now from the information we already have, we know that 3 pounds of hamburger will cost 6 dollars. 

The next thing we need to know is how much one pound of hamburger will cost. This will help us calculate  how much the rest will cost.

we now form an equation to assist us.
3 = 6
1= x

(where x represents the unknown price of one pound of hamburger)

Now we must cross-multiply:

3 * x = 6 x 1

3x = 6 

x = 6/3

x = 2

therefore one pound of hamburger costs 2 dollars.

Now, If one pound costs 2 dollars, how about 510 pounds?

We simply multiply:  510 x 2 = 1,020

Therefore  Samantha will pay 1, 020 dollars for 510 pounds of hamburger.

If you are looking for a word problem heres one.
I have x dollars and I spent $30.83 now I have $85.73 left. What is x?