It shall be the obligation of the grantee to make cable service available to all residents of the city except to the extent that density of homes, adverse terrain or other factors render providing cable service impracticable, technically unfeasible or economically non-compensatory. For purposes of determining compliance with the provisions of this subsection, and to provide for reasonable and non-discriminatory policy governing extensions of cable service within the city, the grantee shall extend service to new subscribers, at the normal installation charge and monthly rate for customers of that classification where there is an average of 40 units per each linear mile of new cable construction. In the event the requirements contained herein are not met, extension of cable service shall be required only on a basis which is reasonable and compensatory.