In a bag, the ratio of red balls to green balls is 4:9. If 7 more red balls are added to the bag, the ratio of red balls to green balls will become 5:6. How many green balls are there in the bag?
Two trains are moving in opposite directions with the same speed. If the length of each train is 120 metres and they cross each other in 12 seconds, then what is the speed (in km/hr) of each train?