If a project has a fee of $1,200 and 18% of the work has been completed, then the Earned Value would be 18% of $1,200 or $216.
The million-dollar question is how the 18% is determined. Typically, it derives from years of experience and from examining what has been produced.
Some folks will look at how many total hours they believe a project or task will take and then compare that to the hours accrued. While this method is not incorrect, it does not account for variation in workers' productivity.
If a highly efficient worker has been on the job, perhaps more than 18% of the work has been completed; conversely, if a low-efficiency worker has been on the job, perhaps less than 18% of the work has been completed.
FYI - Study after study has shown that fixed-fee contracts produce higher profits than hourly contracts.