You should round to the nearest thousand so it would be 138,000+52,000 because the six in 137,638 would round the thousands to seven and 52,091 would round to 52,000 because zero doesn't round up so then you add up 138,000+52,000 and you get your estimated answer.
The best way to estimate it is to do "written addition" in your head, adding 1+8, then 9+3, all the way until you get to the front. the actual answer is 189,459, so your answer should be somewhere close to that.
