Was it c:b or b:c that was 4:5. Oh well, i'll do it with c:b. Either way, you'll figure out the concept
Ok, c:b is 4:5 and b is common to both. So we find a lowest common demoninator for the two bs (5 and 3), which is 15. In a:b, 3 is multiplied by 5 to get 15, so we multiple the two by five...