Question 389337
435 + (n - 1)(-5) = 123 + (n-1)3;
435 - 5n + 5 = 123 + 3n - 3;
440 - 5n = 120 + 3n;
320 = 8n,
n = 40, 
n - 1 = 39, the number of days after which they will weigh the same.
(The Simpsoooon's...taaantantantanantantatananananan.... =D)