There are multi-colored pens in the stationery store. 3/10 of the pens in the stationery store are red and 1/5 are black. There are 12 red pens in the stationery store. Find how many black pens are in the stationery store.
12 3/10 [OP_DIV] 1/5 [OP_MUL]
var_a = 12
var_b = 0.3
var_c = var_a / var_b
var_d = 0.2
var_e = var_c * var_d
print(int(var_e))