Keeping track of the locations of equations with the same answers can be a pretty good test of your memory. The better you are at solving simple equations the easier this task is. This is one reason that it is important for you to master basic arithmetic facts. The less brain power you have to use solving simple problems, the more brain power you have left to deal with more complicated tasks or tasks which involve the use of memory.
Here are a few more basic facts which you should know so well that you can almost immediately recognize the answers:
10 - 2 = 13 - 6 = 4 + 7 = 9 - 5 = 14 - 8 = 12 + 2 = 9 + 3 = 9 - 6 =