It tells us that her house is 5 miles from the Post Office. So we know that each unit on the grid is 1 mile. Lucy walks from her house to the post office to the bank. The shortest path is the hypotenuse of the right triangle. We have one side length. Now, we count the post office to bank's length. It is 12 miles. The Pythagorean theroem is a^2+b^2=c^2 so 5^2+12^2=c^2 Solving this, we get c=13. The shortest path is 13 miles.
