Question

find the relative clause. if it is nonrestrictive, set it off with commas. if it is restrictive, submit the text without making any changes.
prior to becoming the thirty-ninth president of the united states, jimmy carter had to assume control of his familys farm which was struggling to stay operational.

Explanation:

The relative clause "which was struggling to stay operational" provides extra, non-essential information about the specific family farm (already identified as Jimmy Carter's family's farm), so it is nonrestrictive and needs commas around it.

Answer:

Prior to becoming the thirty-ninth president of the United States, Jimmy Carter had to assume control of his family's farm, which was struggling to stay operational.