For solving the numericles in this lesson, following formulas are mosr useful:
lens maker's formula
relations for magnification of optical instruments (however they can be derieved easily by the above equations)
TO find the power of lens, the focal length can be derieved using the image distance and the object distance and the power is found out as 1/focal length in meters
Far point is the maximum distance upto which an eye can focus and near point is the minimum distance upto which an eye can focus.
Sign convension are always better to be understood by a book with proper diagram and an example.