We want to find the solutions for the following system
[tex]\begin{cases}y=10 \\ 3x+4y=19\end{cases}[/tex]We already know the value for the y variable, if we substitute this value on the second equation it is possible to find the x value.
[tex]\begin{gathered} 3x+4\cdot(10)=19 \\ 3x+40=19 \\ 3x=19-40 \\ 3x=-21 \\ x=\frac{-21}{3} \\ x=-7 \end{gathered}[/tex]And those are the results for our system
[tex]\begin{cases}x=-7 \\ y=10\end{cases}[/tex]