Subtract 3 from each side:
3x = -30
Divide each side by 3 :
x = -10
Let's say we're at the store and you want to buy 10 boxes of cookies for a party. Each box of cookies cost 4.89(counting tax), you don't know if you have enough money to buy the cookies with the $65.00 you have with you. You could round the price up to $5.00 and do more simple multiplication. Your total would estimate about $50.00. Now you know you have more than enough money to buy cookies. I hope that makes sense. :)
To do expanded form you just have to do this:
1 7 7
+0.2 +0.5 +0.5
+0.05 +0.02
+0.003
