Answer:
The answer is 250.
Explanation:
Hello! This is a simple subtraction matter. All order-of-operations are opposites (multiplication and division, and addition and subtraction.) This means that since we're presented with a case where 420 + something = 670, the opposite is 670 - 420 = something.
If we compute some simple calculations, 670 - 420 = 250.
There's your answer :)