For length BC, where B(0,3) and C(4,-1) following the axis, length ranges from 0 to 4(according to xaxis) and 3 to -1(according to yaxis) thus 4-0=4,3-(-1)=4 will give u length of 4 for BC.
For length EC, where E(2,-3) and C(4,-1) following the axis,length ranges from 2 to 4(according to xaxis) and -3 to -1(according to yaxis), thus 4-2=2,-1-(-3)=2 will give u length of 2 for EC. (its 4-2 and -1-(-3) not 2-4 and -3-(-1) as length cannot be -ve)
For lengths BF and EF, since BF//EC, BF=2. Since EF//BC, EF=4
