Solve for both systems 5z+x=30 and 9z+7x=80

5z+x=30

5z-5z+x=30-5z

x=30-5z

9z+7x=80

9z+7(30-5z)=80

9z+7(30) (7)(-5z)=80

9z+210-35z=80

210-26z=80

210-26z-210=80-210

-26z=-130

-26z/-26=-130/-26

z=5

x=30-5z

x=30-5(5)

x=30-25=5