Is $18,000 to replace roof with 36 squares of owens corning duration architectural shingles a fair price?

Full roof replacement for 32 squares including: - Tear off of one layer of 30-year-old 3-tab shingles - Installation of Owens Corning Duration shingles with 6 nails per shingle - OC Duration 50-year warranty and 10-year contractor warranty - Ice and water shield installed 6' from eaves, in every valley, and around all perforations - Woven valleys and full ridge vent system - Low pitch and complex geometry included - Additional decking replacement quoted at $70 per sheet of 1/2" CDX if needed

Full roof replacement for a 35 square area including: - Tear off of 1 layer down to plywood - Replacement of up to 2 sheets of damaged plywood - Installation of new drip edges around the perimeter - Ice and water guard along gutter lines and valleys - Synthetic felt underlayment - Owens Corning Durations Lifetime warranty shingles - Rolled roofing for one flat area - Ridge vent and cap on hip and ridge - New pipe boots and step flashing - Painting of pipes on roof - Flash and seal chimney with new metal - Clean up job site and haul away debris

This quote is for roofing work using Owens Corning Duration series materials. - Roof Area: 31 squares - Roof Pitch: 8/12 - Materials: Owens Corning Duration series shingles