Answer :
The equation for the molarity, or molar concentration, is:
[tex]C=\frac{n_{\text{solute}}}{V_{\text{solution}}}[/tex]Where C is the molarity, n is the number of moles of solute and V is the volume of solution.
Since we know the molarity and the volume of solution, we can calculate the number of moles of solute:
[tex]\begin{gathered} V_{\text{solution}}=6.99L \\ C=2.87M=2.87mol\/L \\ n_{\text{solute}}=C\cdot V_{\text{solution}} \\ n_{\text{solute}}=2.87mol\/L\cdot6.99L=20.0613mol\approx20.06mol \end{gathered}[/tex]So, there is approximately 20.06 mol in the solution.