Asmall 12.00 g plastic ball is suspended by a string in a uniform, horizontal electric field. if the ball is in equilibrium when the string makes a 30degrees angle with the vertical, what is the net charge on the ball?

Assume you measured the mass of the cart to be (500 ± 1) g and the mass of the additional mass you put on the cart to be (500 ± 1) g as well. since the scale you are using in the lab cannot measure objects heavier than 600g you will have to sum up individual pieces and propagate the error. so what would be the mass and the standard error of the cart and the mass