$\displaystyle sec{\Theta} = -1.942$

$\displaystyle \frac{1}{cos\Theta} = -1.942$

$\displaystyle \frac{1}{-1.942} = cos\Theta$

$\displaystyle cos^{-1}\frac{1}{-1.942} = \Theta$

$\displaystyle 121^{\circ} = \Theta$

Now that I've got the first value, how do I find the second? All I know is that the CAST rule may be involved, but I don't know how to apply it in this situation. Help on this would be greatly appreciated.