a carpenter is fitting some bookcases to an alcove, using as much of the space as possible from floor to ceiling, a height of 2.5 m. The books to be fitted into the shelves are 210 mm high and a gap of at least 30 mm is necessary above each book so that they can be removed. The shelves are 20 mm thick. The alcove is 1.2 m wide. The bottom shelf should not be less than 300 mm from the ground, as the house-owner cannot bend down easily. How many shelves can be fitted into the alcove?