Question 222733
Let t=tens number and u=units number
10t+u=10u+t-45 
9t=9u-45
t=u-5 for the last 2 numbers
We want the first 2 numbers to be 99 if possible in order to have the largest number possible.
So t+u=9 would be best.
u-5+u=9 substitute u-5 for t
2u-5=9
2u=14
u=7
t=2
The number is 9927
.
Ed