Solve for both systems 10z+9y=183 and 9z + 3y = 129

9z + 3y = 129

9z-9z + 3y = 129-9z

3y = 129-9z

3y/3 = 129-9z/3

y=43-3z

10z+9y=183

10z+9(43-3z)=183

10z+9(43) (9)(-3z)=183

10z+387-27z=183

387-17z=183

387-17z-387=183-387

-17z=-204

-17z/-17=-204/-17

z=12

y=43-3z

y=43-3(12)

y=43-36=7