If latex: \{a_i: i\in i\} is a collection of open subsets of latex: \mathbb{r} , then latex: \cup_{i\in i}a_i is open in latex: \mathbb{r}

(can this be proved without the concept of the open ball from topology)

Which situation could best be represented by this linear equation? 24x + 38y = 520 > if x represents the number of bracelets and y represents the number of rings, there were 24 more bracelets sold than rings. the total sales were $520. if x represents the number of bracelets and y represents the number of rings, there were 38 more bracelets sold than rings. the total sales were $520. if x represents the number of bracelets sold at $24 each and y represents the number of rings sold at $38 each, the total sales were $520 if x represents the number of bracelets and y represents the number of rings, there were 520 bracelets and rings sold. bracelets were $24, and rings were $38. e