2x-3y+4x=19

x-2y+z=9
3x-y+2x=10

I assume you are solving?

multiply the 2nd by 4 and subtract it form the first.
you now have an equation with only x and y

multiply the 2nd by 2 and subtract it from the 3rd.
you now have another equation with only x and y

I assume you know how to solve 2 equations in 2 variables.
To make sure you have the correct solution, sub in your values
in all 3 original equations.