He starts out with $10 * 4 = $<<10*4=40>>40.
James spend $40 / 2 = $<<40/2=20>>20 on the video game.
After buying the game, he has $40 - $20 = $<<40-20=20>>20 left.
He spent $20 / 4 = $<<20/4=5>>5 on the book.
He has $20 - $5 = $<<20-5=15>>15 left.
#### 15