I need help with this.

A frustrated farmer is trying to move a large rock from his land. The stone has a mass of 1275 kg. By using a piece of board as a lever and a fulcrum the farmer will have a better chance of moving the rock. The farmer places the fulcrum 0.288 m from the rock so that the edge of the board is located directly under the center of weight of the rock. The farmer can exert a maximum force of 704.0 N. Calculate the minimum total length of board needed to move the stone?