I have sold 2/3 of my pencils for $ 0.15 each . If i have 8 pencils left how much money did i collect for the pencils i sold.

We don't know the total number of pencils, therefore we'll
put the total number of pencils as x.

If you've sold
(2/3)*x, you've had (1/3)*x left.

We know, from enunciation
that the amount of left pencils is 8.

We'll put (1/3)*x =
8.

We'll cross multiply and we'll
get:

x = 8*3

x = 24
pencils

Now, we'll found the amount of sold pencils, namely
2x/3.

We'll substitute x by 24 and we'll
get:

2*24/3 = 2*8 = 16 pencils
sold

To compute the cash earned for sold
pencils, we'll multiply 16 by
$0.15.

16*0.15 =
$2.40