The value of angle ABC is 74.2°
To find the measure of angle ABC we use sine rule.
Sine rule is used when two angles or two sides are given.
x is an unknown angle and two sides are given
Mathematically, sine rule states that;
a/sinA = b/sinB
20/sinx = 18/sin60
20sin60 = 18sinx
17.32 = 18sinx
divide both sides by 18
sinX = 17.32/18
x = sin⁻¹( 0.962)
x = 74.2°
Therefore the measure of angle ABC is 74.2°