Then the original two digits are10 (9-x)+X.
After exchanging the number in one number with the number in ten numbers
The two digits of are10x+9-x.
From the title,10x+9-x =10 (9-x)+x+9.
The solution is x=5.
There are X toys in the nail box.
Then box b has x+40.
Then x+40+7=3(x+5)
The solution is x= 16.
If there are x chickens, there are 100-x rabbits.
Then 2x-4( 100-x)=80.
The solution is x=80.