Holding Time of Athletes A group of ten athletes were tested for isometric endurance by measuring the length of time they could resist a load pulling on their legs while seated. The approximate amount of time (called the holding time) that they could resist the load was given by the formula 

t = 31,293w^-1.5,
where w is the weight of the load in pounds and the holding time t is measured in seconds.
(Townend, M. Stewart, Mathematics in Sport, Chichester, Ellis Horwood Limited.)
(a) Determine the holding time, to the nearest second, for a load of 25 lb. 

(b) When the weight of the load is doubled, by what factor is the holding time changed?