2014 AM Q10D(Realized P/L) - Is answer wrong?

IS is the biggest pile of crap in level-III, worse than GIPS.

No formulas, all conjecture and vague math to prove it’s pretty difficult to implement large trades. Phantom costs suck and so does IS

Even I got trapped in this. Why didn’t they use the Benchmark Price in the denominator (which is Monday’s close price)?