Answer:
BC = 8 cm
Explanation:
tan(x) = sin(x)/cos(x)
sin(x) is the opposite side of the angle x.
cos(x) is the side with a right angle to sin(x).
2 = 12/EC
EC = 12/2 = 6 cm
=>
CD = ED - EC = 10 - 6 = 4 cm
now, the same tan(x) relation had to be true for BCD.
tan(x) = BC/CD
2 = BC/4
BC = 8 cm