laravel proplem with Model::with appended column

i try to add appended column with Model::with

$pitchChech =  Pitch::with(['prices'=>function ($query){
            $query->select('*',\DB::Raw("(select sum(HOUR(TIMEDIFF(valid_to ,valid_from))) from pitch_price as xpitch_price where pitch_id = pitch_price.pitch_id ) as x "))
            ->whereRaw(" x < ?",[24]);
        }])->get();
      dd($pitchChech);

and i have this output

SQLSTATE[42S22]: Column not found: 1054 Unknown column 'x' in 'where clause'  

i can't understand what is the problem im using laravel 5.1 but i don't think there are problem with ut

via Chebli Mohamed