Which pair of measurements is not equivalent?

160 oz., 10 lb.
5 lb., 80 oz.
14,000 lb., 7 tons
4 tons, 6,000 lb.

If you would like to know which pair of measurements is not equivalent, you can calculate this using the following steps:

1 lb = 16 oz
1 ton = 2,000 lb

10 lb = 10 * 16 oz = 160 oz
5 lb = 5 * 16 oz = 80 oz
7 tons = 7 * 2,000 lb = 14,000 lb
4 tons = 4 * 2,000 lb = 8,000 lb

Not equivalent: 4 tons, 6,000 lb.