First, decompose 1620 by the method of decomposing prime factors, and then combine the decomposed prime factors by age, which is 3 years older than the last one. Because1620 = 2× 2× 3× 5 ... decomposition = 9× 12× 15 ... combined, Lele 15 years old, obviously 12 years old, Hong Chen 9 years old.

equation

Let one of them be x (x-3) * x * (x+3) =1620x3-9x =1620x =12, then (x-3) = 9x =12 (x