Cuatro amigos decidieron ir hacer ejercicio a una ruta de caminata libre. Primero vieron el recorrido en un croquis

Since it takes her 2 1/2 miles to get to the aquarium from her hotel, you need to subtract the various distances from  this value in order to find how long it took Clara to walk the rest of the way to the aquarium. 

2 1/2 - (1/4+1 3/4)= 2 1/2 - 2= 1/2

Clara must walk 1/2 a mile to get the rest of the way to the aquarium.