To solve this, we first need to substitute the value of b from the first equation into the second equation:

a - 4 = 8

Now, we can solve for a by adding 4 to both sides:

a = 12

Now that we have found the value of a, we can substitute it back into the first equation to find the value of b:

12 - b = 4

Subtracting 12 from both sides gives us:

b = 8

So, the solution is a = 12 and b = 8.

To check this solution, we can substitute the values back into the original equations:

a = 12, b = 8

12 - 8 = 4 (true)
12 - 8 = 4,8 (true)

Therefore, the solution is correct.