Solve for 3u+z=15 and u+2z = 10

u+2z = 10

u+2z-2z = 10-2z

u= 10-2z

3u+z=15

3(10-2z)+z=15

3(10) (3)(-2z)+z=15

30-6z+z=15

30-5z=15

30-5z-30=15-30

-5z=-15

-5z/-5=-15/-5

z=3

u= 10-2z

u= 10-2(3)

u= 10-6=4