In order to calculate the distance from Oceanfront to Seaside, let's first consider the vertical distance from Seaside to Landview, then the horizontal distance from Landview to Oceanfront.
After that, we can use the Pythagorean theorem to calculate the distance from Oceanfront to Seaside, since this distance is a hypotenuse of a right triangle created by the three cities.
So we have:
Therefore the distance is about 40 miles, so the correct option is the fourth one.