Answer
-0.4
Work Step by Step
As we have seen examples of, we know that $\cos$ 120$^{\circ}$ = -$\frac{1}{2}$
Therefore: $cos$ 120$^{\circ}$ = -0.5
So, as the angle of $\cos$ gets larger, the result gets smaller. Therefore, $\cos$ 115$^{\circ}$ would be slightly more than $\cos$ 120$^{\circ}$.
-0.4 is the option closest to -0.5
