Eratosthenes' most famous accomplishment is his measurement of the circumference of Earth. ... Eratosthenes then measured the angle of a shadow cast by a stick at noon on the summer solstice in Alexandria, and found it made an angle of about 7.2 degrees, or about 1/50 of a complete circle.
hope it helps.
u = -(6/7)w
place all values with 'u' on one side of the equation.
4u + 8w = - 3u + 2w
4u + 3u = 2w - 8w
further simplify the equation by solving the addition and subtraction.
7u = - 6w
make 'u' the independent variable by placing its co-efficient on the right-hand side.
u = - (6/7)w
the diver is 33 feet below the surface.