Answer:
490+70x=670+40x
Explanation:
This is almost exactly the same as the pizza/giftcard question. But here Tom and Tammy are saving money, so ADD the monthly amount. 70x for Tom and 40x for Tammy.
Tom's account:
490 + 70x
Tammy's account:
670 + 40x
When they say "when the two accounts have the same amount of money" SET them EQUAL to each other.
490+70x=670+40x