This is due to the fact that 1.5 tons is literally 3,000 pounds and someone would have to be morbidly obese to weigh that much, 50 lbs. is underweight for an adult, 160 oz is 10 lbs which is even more underweight, which leaves 180 lbs as the last resort as well as the one that makes the most sense.
Just square the top and bottom of the fraction. 
and 
so we have 12/16 and then we reduce to 3/4
