To calculate the cosine of angle θ we need the law of cosines:
c²=a²+b²-2*a*b*cosθ.
In our case a=7, b=8 and c=11. We solve for cosθ:
-2*a*b*cosθ=c²-a²-b², we divide by -2*a*b and get:
cosθ=(c²-a²-b²)/(-2*a*b)=-1/14=-0.07.
So the correct answer is B -0.07.