Six friends, Alex, Ben, Cal, Dan, Elmer and Frank need to cross a river in a small canoe. The canoe can only carry a maximum of 130 kg.

Al weighs 120 kg, Ben weighs 110 kg, Cal weighs 90 kg, Dan weighs 80 kg, Elmer weighs 50 kg, Frank weighs 40 kg and they have 20kg of supplies.

How do they get across in a minimum number of steps?