You do 3/5 minus 3/5 which cancels out to 0. Then you do 6 minus 4 which is 2. The answer is 2.
To find AB(x) and BC(y), you can do(there are multiple ways you can do this):
tan A = 
tan 60° =
or (tan 60°) · 7 = y
tan 60° = 
√3 · 7 = y
7√3 cm = y
sin B = 
sin 30° =
or 
sin 30° =
= 
x = 
x = 14 cm
AB = 14cm
BC = 7√3 cm
590. Since 2 is under 5 you round it down