Question 123680
So, we need to change the words into mathematical operations.The problems says:
A+B=147 and A-B=43, so we take the second equation and write it down:
A-B=43 so we need to find what A is A=43+B 
We replace the A from this ecuation into the first ecuation so instead of A+B=147, we will have 43+B+B=147 so 2B=147-43 and 2B=104 so B=104/2 which equals 52. Now we replace B in any of these ecuations with the value 52 and solve the ecuation to find A. The rule is from one ecuation find one of the unknown values and replace it into the other ecuation. 
Try this way, it may work.