Great! Now that you've got your 3 main costs figured out, let's put them together in order to find the total cost of your trip.

```
def double(n):
return 2 * n
def triple(p):
return 3 * p
def add(a, b):
return double(a) + triple(b)
```

- We define two simple functions,
`double(n)`

and`triple(p)`

that return 2 times or 3 times their input. Notice that they have`n`

and`p`

as their**arguments**. - We define a third function,
`add(a, b)`

that returns the sum of the previous two functions when called with`a`

and`b`

, respectively.