two objects A and B separately weigh 75g and 45g respectively on a spring balance. A and B together weigh 120g while the difference of their weights is 30g. considering the four weights and assuming...

two objects A and B separately weigh 75g and 45g respectively on a spring balance. A and B together weigh 120g while the difference of their weights is 30g. considering the four weights and assuming the weights are independent with a constant variance, obtain the least square weights of A and B.