The problem is kamala had 5,026 grams flour in a canister.she brought a 4,158 gram bag of flour.she poured some flour from the bag to the canister.as the results the mass of the flour in the canisteris now twice the mass of the flour left in the bag.how much flour is in the bag now?

Ah ha !  A nice problem.  You need to read it slowly and carefully
to avoid getting tangled up and falling down.       

Originally in the can:        5,026 .
Amount poured from the bag:        ' F '  (for 'flour')
New amount in the can:              5,026 + F
New amount in the bag:              4,158 - F

You said there's twice as much in the can as there is in the bag,
so you can write
                                             5,026 + F  =  2 (4,158 - F)

Eliminate parentheses on the right side:  5,026 + F  =  8,316 - 2F

Add  2F  to each side:                              5,026 +  3F  =  8,316

Subtract  5,026  from each side:                            3F  =  3,290

Divide each side by  3 :                                            F  =  3,290/3

Amount in the can = 5,026 + F  =   6,122 and 2/3

Amount in the bag = 4,158 - F  =   3,061 and 1/3

Check:

         (6,122 and 2/3) / (3,061 and 1/3)  =  2              yay!

I don't know why the question-writer picked such weird numbers.
In order to actually go through the process that's described, you'd
need to be able to measure differences of 1/3 gram out of almost
13-1/2 pounds of flour ... a measurement accuracy of 0.005 % !
But my arithmetic is bullet-proof.

15 dollars because half of 30 is 15.