6. A rabbit farm has some adult rabbits and baby rabbits. The number of baby rabbits is 4 times that of the adult rabbits. After a period of time, some baby rabbits grew into adult rabbits. As a result, 60 baby rabbits grew into adult rabbits, and at this point, the number of adult rabbits and baby rabbits became the same. So, originally, there were ( 
 adult rabbits.
40
【Answer】After a period of time, the number of small rabbits decreased by 60, and the number of large rabbits increased by 60; the difference is 120, which corresponds to the original number of large rabbits being $4-1=3$ times; thus, the original number of large rabbits is $120 \div 3=40$ (only)