I can't seem to figure this out.
The mass of 3 notebooks and 1 box is 610g. Each notebook is 250g lighter than the box. What is the mass of each notebook?
This seems to be $3(x-250)+x=610$. So, $3x-750+x=610\implies 4x-750=610\implies 4x=1360\implies x=1360/4 = 340$
Which seems to be impossible, since $3x$ (if each $x$ is $340$) is more than 610g.