In a triangle ABC, you have AB with a side length of 5, side BC with a length of 6 and side AC with a length of 7. Will this form a triangle? How do you know?

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.