Answer:
C
Step-by-step explanation:
140
14x10 =140 -- pretend your doing 14 x 1 then put the 0 from the 10 to the 14.
A half-life of 9 minutes corresponds to a decay factor <em>k</em> such that

Then the time it takes for the substance to decay from 610 g to 124 g is time <em>t </em>such that

Solve for <em>t</em> :



so it takes about 20.7 min for the 610 g sample to decay down to 124 g.