Solve    (1/5)x + 1/3 = (2/5)( x + 4 )

We need to ditch the 3 and the 5... 
So, multiply both sides by
3x5 = 15...

15 ( (1/5)x + 1/3 ) = 15 (2/5)( x + 4 )

Here's where I don't want you to make the mistake! 
Think about it!

(15/5)x + 15/3 = ( (15)(2)/5 )( x + 4 )
No, you do NOT multiply the 15 into this!               

3x + 5 = 6 ( x + 4 )  which gives  3x + 5 = 6x + 24 <-be careful here!  Ditch the 3x...  3x - 3x + 5 = 6x - 3x + 24  which gives  5 = 3x + 24  ditch the 24...  5 - 24 = 3x + 24 - 24  which gives  -19 = 3x  ditch the 3...   -19/3 = 3x/3  which gives  -19/3 = x