Help! College final issues.

M
Okay this has nothing to do with periods or anything but I have a question. 
I'm in college and I'm at the end of the semester in my political science class. I have a C in the class which is passing. I can take the optional final exam. If I take the optional final exam and I get a 79 or higher I can make a B in the class. If I don't take the final I stick with a C in the class. I have failed 3 out of 4 exams. So I'm not so confident I'm gonna score high enough for a 79. 
So should I spend time studying and trying for a 79 or higher to make a B or should I keep the C and focus on other finals? 

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