In your linear model, the hypotheses “the utility of a person living on 1 resource is 0” and “doubling resources doubles utility” imply that utility is always 0. Maybe you meant the second hypothesis to be “doubling the number of resources beyond the first doubles utility”, so that a person’s utility is 0.1 times the number of resources beyond the first. In this version of the linear model, the total utility of population A is 9 (0.9 utility per person), and the total utility of population Z is 0.1 (approximately 0.001 utility per person).
In your linear model, the hypotheses “the utility of a person living on 1 resource is 0” and “doubling resources doubles utility” imply that utility is always 0. Maybe you meant the second hypothesis to be “doubling the number of resources beyond the first doubles utility”, so that a person’s utility is 0.1 times the number of resources beyond the first. In this version of the linear model, the total utility of population A is 9 (0.9 utility per person), and the total utility of population Z is 0.1 (approximately 0.001 utility per person).