Solve this im stuck please solve!

72 miles

Step-by-step explanation:

To solve this problem, you can use the pythagorean theorem, which is a^2 + b^2 = c^2. We already have b equal to 54 miles, and since c is the hypotenuse, it equals 90 miles. We can substitute the values into the formula to get:

a^2 + 54^2 = 90^2

a^2 + 2916 = 8100

a^2 = 5184

a = 72 miles