You have that the number is written xy

and also x+y  = 12 (i)

also x is 2 greater than y since x is the 10's and y is the one digit, thus

x-y =2 ( ii )

This is a system of linear equations, I isolate x in (i)

x = 12-y and insert that into (ii)

12-y-y = 2 <=> 12-2y = 2 <=> 12-2 = 2y  <=> 10 = 2y <=> y = 5

Now I insert that back into (i):  x+5 = 12  <=>  x = 12-5 <=> x = 7

I check my solution, the sum is 5+7 = 12 ok

the 10 digit is 7 which is 2 greater than 5 ok