koori

alright, i want an explanation on how to do these so i can do the rest on my own... the first problem is j/3 = 2/5 how do i solve that?

can someone help me solve this? not just an answer but a method of solving cause im having a hard time grasping this. Three times the larger of two numbers is equal to four times the smaller. The sum of the numbers is 21. Find the numbers.