Hi,

It is quite straightforward forward and you can do it in two ways..
1) Algebraic..
100 for X but sold for 50..
Thus overall profit is (50-x)..
But we are looking for profit per piece = $\frac{50-x}{100}=0.5-\frac{X}{100}$
E
2) substitute a value for X
Let X = 40
So profit = 50-40=10
Per piece = 10/100=0.1
Check choices for this answer..
Only E gives you 0.1 as answer 0.5-40/100=0.5-0.4=0.1
E