2z+5x=18 10z+x=42

10z+x=42

10z-10z+x=42-10z

x=42-10z

2z+5x=18 sub in x and solve for z

2z+5(42-10z)=18

2z+210-50z=18

210-48z=18

210-210-48z=18-210

-48z=-192

-48z/-48=-192/-48

z=4

x=42-10z

x=42-10(4)

x=42-40

x=2