For this case we have a function of the form:
 
 Where,
 A: initial amount
 b: growth rate
 x: time in minutes
 Substituting values we have: 

 By the time the sample weighs 583.8 g, we have: 

 From here, we clear x: 
 
 
 Answer:
 the sample will weight 583.8 g at 276 minutes