When the box containing 10 cups was weighed, it was 3.1 kg (kg). When you removed one cup from this box, its weight changed to 2.81 kilograms (kg). Find the weight of the empty box in kilograms (kg).
3.1 3.1 2.81 [OP_SUB] 10 [OP_MUL] [OP_SUB]
var_a = 3.1
var_b = 3.1
var_c = 2.81
var_d = var_b - var_c
var_e = 10
var_f = var_d * var_e
var_g = var_a - var_f
print('{:.2f}'.format(round(var_g+1e-10,2)))