Wat is the smallest number of whole logs p 725 kgm3

Question

Here is the problem which I am struggling on, please help me!

Problem: What is the smallest number of whole logs (p = 725 kg/m³, radius = 0.0558 m, length = 3.20 m) that can be used to build a raft that will carry four people, each of whom has a mass of 90.0 kg?

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