Mall is 3 mile west and 2 mile south : Both these two forms sides of right Angle triangle & hence using Pythagoras theorm we can say that Mall is (3^2+2^2) ^0.5 = Sqrt(13) miles = 3.6 miles Southwest to the city centre .

Park is 4 miles east and 5 mile north : Both these two forms sides of
right Angle triangle & hence using Pythagoras theorm we can say
that park is (4^2+5^2) ^0.5 = Sqrt(41) miles = 6.40 miles Northeast to the city centre .

Hence total distance between them = 3.6 +6.4 =9.9 miles (answer)