### Home > CC4 > Chapter 1 > Lesson 1.1.1 > Problem 1-6

In what order must she put the machines to get a final output of 5?

Substitute 6 for

*x*in the first function.*y*= 1Let the output from the first equation become the input,

*x*, in the second equation.*y*= 1² − 6*y*= −5

Incorrect. Try the other order.Substitute 6 for

*x*in the 2nd equation.*y*= 6^{2}− 6

*y*= 30Let the output from the second equation become the input,

*x*, in the fist equation.*y*= 5

Correct!Is it possible for her to find an initial input that will get a final output of

? If so, show how she could do that. If not, explain why not.

Which equation cannot have a negative output? What input would you need from the other equation to get −5 as an output? See part (a) for more help.