There are buses that depart only when there are more than 15 and no more than 30 people. If there are 9 people on the bus right now, find out how many more people need to get on the bus before it starts.
15 1 [OP_ADD] 9 [OP_SUB]
var_a = 15
var_b = 1
var_c = var_a + var_b
var_d = 9
var_e = var_c - var_d
print(int(var_e))