mathematics

Alex collected 3 times as many seashells as Clay.
When Alex gave Clay some of his seashells, they each had 14.
How many seashells had Alex given to Clay?

$\begin{array}{|lrcll|} \hline (1) & A &=& 3C \\ (2) & A-x &=& 14 \\ (3) & C+x &=& 14 \\ \hline (2)+(3) : & A+C &=& 28 \\ & 3C +C &=& 28 \\ & 4C &=& 28 \\ & \mathbf{C} &=& \mathbf{7} \\ \hline & A &=& 3C \\ & A &=& 3*7 \\ & \mathbf{A} &=& \mathbf{21} \\ \hline & C+x &=& 14 \\ & 7+x &=& 14 \\ & \mathbf{x} &=& \mathbf{7} \\ \hline \end{array}$

7 seashells had Alex given to Clay