We can rewrite the phrase for every '1 red light there are 9 blue lights' as there are 9 blue lights for every red, which may make it slightly clearer.
If there are 7 red lights, and 9 blues for every red, then there are 7*9 blue lights, or 63 blue lights. Now we can add the red and blue lights; 63+7=70, so there are 70 lights in all.
