HI OTT62,
"What I am looking for is to be able to set my margins at say, 30% then the sale price is then automatically set after selecting a 30% margin. Is that possible?"
SG provided the formula to do exactly that in the FIRST reply to your question. (That reply should be marked "solved")
Here's a table showing the results for a variety of Margin settings, Your 910 example is highlighted, as is 30%, 50%, 75% and 100% (impossible to achieve unless your cost was zero, and even then impossible to calculate due to division by zero).
I've included a chart showing all of the percentage margin results from 1 to 99 in one percent steps.

Your syntax error may have resulted from including the = sign at the beginning when entering the formula.
Select the cell, tap = to open the Formula Editor, enter all of the formula, NOT including the opening =, click the green checkmark to confirm the formula.
Regards,
Barry