AB/2 +BC +CD +DE +EF/2 =6a
BC/2 +CD +DE/2 =4a
AB/2 +BC/2 +DE/2 +EF/2 =2a
AB +BC +CD +DE +EF =7a
AB +BC +DE +EF =4a
CD =3a
AB/2 +BC +CD +DE +EF/2 =6a
BC/2 +CD +DE/2 =4a
AB/2 +BC/2 +DE/2 +EF/2 =2a
AB +BC +CD +DE +EF =7a
AB +BC +DE +EF =4a
CD =3a