Answer:
Nabila has $25 dollars.
Hasan has $19 dollars.
Tarek has $50 dollars.
Explanation:
Let's say Hasan has "x" dollars at first. The question tells us that Nabila has six more dollars than Hasan has. This means that Nabila has "x + 6" dollars. The last given information is that Tarek has two times what Nabila has. So, Tarek has "2x + 12" dollars, basically.
Then, we can add up all these amounts to find out the result for each person.

We found what is "x". This means that we actually found the answer.
Hasan had "x" dollars so he has $19 dollars.
Nabila had "x + 6" dollars so she has $25 dollars.
Finally, Tarek had "2x + 12" dollars or two times of what Nabila has so he has $50 dollars.