Answer: 10.99
Work Shown:
Angle B = 20 is the reference angle
AC = 4 is the side opposite this reference angle
BC = x is the unknown adjacent side
tan(angle) = opposite/adjacent
tan(B) = AC/BC
tan(20) = 4/x
x*tan(20) = 4
x = 4/tan(20)
x = 10.9899 approximately (make sure your calc is in degree mode)
x = 10.99 rounding to two decimal places
BC = 10.99