Final answer:
To add rational expressions, find a common denominator and then add the numerators.
Step-by-step explanation:
To add rational expressions, we need to have a common denominator. In this case, the common denominator is (x + 3)(5x + 15). We can rewrite the fractions with this common denominator: (x(x + 3))/((x + 3)(5x + 15)) + (3(5x + 15))/((x + 3)(5x + 15)). Now, we can add the numerators: (x(x + 3) + 3(5x + 15))/((x + 3)(5x + 15)). Simplifying the numerator, we get (x^2 + 3x + 15x + 45)/((x + 3)(5x + 15)). Combining like terms, we have (x^2 + 18x + 45)/((x + 3)(5x + 15)). This is the simplified form of the sum of the rational expressions.