How many?

Slugs

The slug is a derived unit of mass in a weight-based system of measures, most notably within the British Imperial measurement system and the United States customary measures system. A slug is defined as the mass that is accelerated by 1 ft/s2 when a net force of one pound (lbf) is exerted on it.

Tonnes

The tonne is a metric unit of mass equal to 1,000 kilograms. It is also referred to as a metric ton to distinguish it from the non-metric unit. It is equivalent to approximately 2,204.6 pounds.