155075

You have to add the same number to so that you have a number on the left that divides by 3 and a number that divides by 4 on the right. When you have got this you have to divide the number on the left by 3 and the number on the right by 4. If x=19 then the number on the left is 39 and the number on the right is 52. If you divided these by three and four respectively you get an answer of 13. So the answer is 19