Start with the second equation, which tells you that *t* = 4.

If *t* = 4, then you can rewrite the first equation as follows (and solve):

4*u* – *u* = 18

3*u* = 18

*u* = 6

from Tumblr https://ift.tt/2oP7c55

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Start with the second equation, which tells you that *t* = 4.

If *t* = 4, then you can rewrite the first equation as follows (and solve):

4*u* – *u* = 18

3*u* = 18

*u* = 6

from Tumblr https://ift.tt/2oP7c55