Solution: Let total articles be $ x $. $ 0.6x = 45 $. Divide: $ x = \frac{45}{0.6} = 75 $. \boxed{75}Question: If $\frac{a + b}{a - b} + \frac{a - b}{a + b} = 3$, find the value of $\frac{a^2 + b^2}{a^2 - b^2}$.