ANSWER:
[tex]-8x-10y=-42[/tex]STEP-BY-STEP EXPLANATION:
We have the following system of equations
[tex]\begin{gathered} 4x+5y=21 \\ 3x-10y=15 \end{gathered}[/tex]If we want to make the coefficient of y equal, we must divide the two quotients, like this
[tex]\frac{-10}{5}=-2[/tex]Therefore we multiply by -2, the first equation
[tex]\begin{gathered} -2\cdot4x+-2\cdot5y=-2\cdot21 \\ -8x-10y=-42 \end{gathered}[/tex][tex]undefined[/tex]