Percent yield is calculated using:
[tex]percent \: yield = \frac{actual \: yield}{theoretical \: yield} \times 100\%[/tex]
Your actual yield is how much you actually had at the end of the experiment = 79g.
Your theoretical yield is how much you calculated you should have gotten in an ideal, perfect experiment = 104g.
So put those values into the equation:
[tex]percent \: yield = \frac{79}{104} \times 100\% = 76\%[/tex]
