Answer:
A number: since we don't know what the exact number is we can represent that number with a variable. Let's use x...
x + (-3) = 8
You can also write this as...
x - 3 = 8
They both mean the same thing :)
When you solve...
x - 3 = 8
add 3 on both sides...
x = 11
Your answers are...
x + (-3) = 8
x = 11
Hope this helps :)