During a math test, Young-hee mistakenly added 0.42 which should have been subtracted, and submitted 0.9 as the answer. What is the original correct answer?
0.9 0.42 [OP_SUB] 0.42 [OP_SUB]
var_a = 0.9
var_b = 0.42
var_c = var_a - var_b
var_d = 0.42
var_e = var_c - var_d
print('{:.2f}'.format(round(var_e+1e-10,2)))