we can write the original number like this:
x*10+y,
where x and y are the digits, so the number would look like this: xy
and we know that if we inverse, i.e. y*10+x, we will get the original number plus 36:
y*10+x=x*10+y+36
let's move all the ys and xs to the left:
10y-y+x-10x=36
9y-9x=36
let's divide by 9:
y-x=4
so the difference between the digit is 4, and x is smaller
this could mean that it could be any of these numbers:
15
26
37
48
59
next possibility: x=6 woould make y=10, so it would no longer hold.