Question 1184485
The way the description is made, the two machines do not operate together at the same time.  The only the new machine first is used, and then only the old machine is used.


The job seems to be,  "complete one-half mile of cement road".  That is the ONE job.


x, the amount of time the old machine was in use.
{{{(1/12)4+(1/16)x=1}}}
Simplify and solve.