160079

Basically, the calculator reverses the steps. For example;

Say my ending number was 3, the calculator would add 7, divide by 2 and subtract 4, instead of adding 4, multiplying it by 2 and subtracting 7 which we needed to do.

So in fact, my starting number, if my ending number was 3, would be 1 because;

3 add 7 = 10
10 divide by 2 = 5
5 subract 4 = 1