Call Brianna is B,Shanita is S.

B+S=24.00

B-2S=3.00

2B-2S=6.00

 B is:(24.00 x 2)+6.00}:2:2=13.50

S is:24.00-13.50=10.50

Deduced Brianna has 10.00 more than Shanita

Let B and S be the amount of money of Brianna and Shanita in dollars respectively.We have :

\(\left\{{}\begin{matrix}B+S=24.00\\B-2S=3.00\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}\dfrac{1}{3}B+\dfrac{1}{3}S=8.00\left(1\right)\\-\dfrac{2}{3}B+\dfrac{4}{3}S=-2.00\left(2\right)\end{matrix}\right.\)

(1) - (2) = B - S = 10.00

So,Brianna has 10.00 dollars more than Shanita.