D is correct. you’re welcome.
Step-by-step explanation:
here,,
a=3,b=10,C=120°
c^2=a^2+b^2-2ab cos120°
=(3)^2 +(10)^2 _2 (3)(10)(-1/2) [cos120°=-1/2]
=9+100-(-30)
=109+30
=139
c=(139 )1/2=11.79
c=12
-6/7 = -x/84
84/7 = 12
12(-6) = -72
x = -72
So, -6/7 = -72/84 because -72/84 simplifies to -6/7
