To determine the distance between the bank and Hiroto's place you have to determine their location first.
Each unit represents 1 mile.
The dot that represents Hiroto's place seems to be in the middle of the square between 3 and 4 miles (over the x-axis) so its location is (3.5, 6)
The dor that indicates the Bank is almost over the line of -8, we can say it's around -7.9, so the coordinates for it's location are (-7.9, 6)
To calculate the distance you have to subtract them:
The distance between Hiroto's house and the bank is arround 11.4 miles