3- (20 points) Using the following values for the microscopic scattering cross sections for hydrogen and oxygen, of' = 20.1 barns and o. = 3.8 barns respectively, and the definition of average lethargy gain per collision } = 1- (A-1)2 -In calculate average lethargy gain 2A per collision for water H20 Average lethargy gain per collision of a substance containing more than one material is given as: = ($6.95,1 +$225,2 + .-ns,n) ... where 1, 2.. shows different atom species