It seems that I haven't studied equations in primary school, so the problem that a one-dimensional equation can explain is complicated. Here, I use backward calculation method to calculate the formula in Note: [] Step by step to help me understand, so I don't need to write it.

The peaches of the last two monkeys: B monkey (26-2)/2= 12 A monkey 12+2= 14.

Before "A returns to B five monkeys": [A monkey 14+5= 19] B monkey 12-5=7.

Because of "stealing half of Monkey B": [Monkey B 7*2= 14] Monkey A 19-7= 12.

Monkey B saw that Monkey A took too much, so he grabbed half of it. At first Monkey A was 12*2=24.

So at first the monkey took 24.