Answer:
19.38 = AB
Explanation:
use law of sines, we get,
18/sin(60) = 20/sin(B)
sin(B) = sin(60)(18)/(20)
so angle B = 51.21
the total angle for triangle is 180 so 180 - 60 - 51.21 = 68.79
again using law of sines,
AB/(sin(68.79)=18/sin(60)
AB = 19.38