P(ABCD) = AB + BC + CD + AD
P(ADEF) = AD + DE + EF + AF
FE = BC
P(ABCD) - P(ADEF) = AB + CD - DE - AF = 2 + 5 - 1 - 4 = 2
P(ABCD) = AB + BC + CD + AD
P(ADEF) = AD + DE + EF + AF
FE = BC
P(ABCD) - P(ADEF) = AB + CD - DE - AF = 2 + 5 - 1 - 4 = 2