Describe a situation that could be modeled by x≤50

Let x be the number of people you can seat in an auditorium. If there are 50 seats max, then you can seat up to 50 people. This means that x can be smaller than 50 or equal to 50.

To write it out in shorthand, we simply say  (x is less than or equal to 50)

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.