Dropping a course

In my initiative calculus class there are only 4 grades. Which are all exams 20 % each the final being 40% of the total grade. If I fail my first exam is there a chance I can still make it out of the course with at least a passing grade (c-). I know I should always aim for the best but if my best isn’t good enough would my best bet be to drop the course ?

0.2 x first exam grade + 0.2 x second exam grade + 0.2 x third exam grade + 0.4 x final exam grade = overall grade

Say you got 55% on the first exam and 100% on everything else.

0.2 x 55 + 0.2 x 100 + 0.2 x 100 + 0.4 x 100 = 91

So plug in some reasonable numbers alongside your real first exam grade and see what you’d have to get on each exam to get at least a C-.