Can you give a guesstimate of how much it will cost to fix my car?
你能估计出修理我的车要花多少钱吗？

You could then guesstimate how many stores there were nationwide, based on the number of stores per 100,000 people in each of the cities you counted.
然后根据你数过的每个城市中每10万人有多少电话商店，估算一下全国共有多少家这种商店。

Or did you zero in on the two most important problems--how deep is the Mariana Trench and how fast might a cannonball fall through the water-- then hazard a guesstimate?
或者，你是否集中考虑两个最重要的问题－-马里亚纳海沟有多深，炮弹在海水中下沉的速度有多快－然后冒险作出猜测？