how can i fix this swift code

I am self learning swift. I do know how to solve this error in c++ but don't really know how to fix it in this language.

i get this error -> Use of unresolved identifier 'calculateDistance'

import Foundation

struct location {

let x: Int

let y: Int

}

struct deliveryArea {

let center: location

let radius: Double

func contains (_ location: location) -> Bool {

let distanceToStore = calculateDistance(from: location, to: center)

if distanceToStore < self.radius {

return true

}

}

}

let restaurant1 = deliveryArea(center: location(x: 2, y: 3), radius: 2.5)

let restaurant2 = deliveryArea(center: location(x: 7, y: 8), radius: 1.5)

let restaurants = [restaurant1, restaurant2]

func calculateDistance (from source: location, to target: location) -> Double {

let distanceX = Double(source.x - target.x)

let distanceY = Double(source.y - target.y)

let result = sqrt(pow(distanceX, 2.0) + pow(distanceY, 2.0))

return result

}

func isInDeliveryLocation (location: location) -> Bool {

for restaurant in restaurants {

if restaurant.contains(location) {

return true

}

}

return false

}