Find the exact value of the expression using the provided information. Find cos(s + t) given that cos s = -1/6. With sin quadrant III, and cos t = -3/5, with t in quadrant III.
a. 3-4√37/30
b. 3 + 4 √35/30
c. -3 - 4√35/30
d. 3 - 4 √35/30