1. The problem statement, all variables and given/known data A tunnel cross-section is to have the shape of a rectangle surmounted by a semicircular roof. The total cross-sectional area must be A, but the perimeter minimised to save building costs. Find its dimensions 2. Relevant equations 3. The attempt at a solution I have that the perimeter would equal pi*r + 4r + 2h (where r is the radius of semi circle, h is height of rectangle) and that A=0.5pi*r^2 + 2rh, but am unsure as to how to get started. Any help would be appreciated.