An underground mass of salt may form a dome trapping a petroleum reservoir. Compute the gravitational anomaly (deviation of gravitational acceleration) produced by an underground salt mass, where for simplicity we assume that the salt (density 2220 kg/m³) forms a sphere of radius 0.5 km centered 0.5 km beneath the surface, and compute the gravitational anomaly by determining the difference from a corresponding mass of granite (density 2640 kg/m³). Express your answer in m Gal = 10⁻⁵ m/s². (Gravity data can be measured to a precision of ∼ m Gal.)