Alright, since you know the two shapes are similar, this means the scaling ratios are the same, and all sides will produce the same fraction when compared to one another, e.i : LK to BA. You start by making a fraction of the two sides with lengths you know, giving you the fraction 10/3 from BA to LK. Then by cross multiplying in the equation below you get the answer of :
10/3= 4/y to 10y=12. then by dividing by 10 you get the answer of 1.2 cm or A