To solve the subtraction problem 86639 - 436, we follow these steps: Start from the rightmost digit (ones place) and move left. In the ones place, we subtract 4 from 6, which gives us 2. In the tens place, since there is no tens digit in 436, we simply take the digit from 86639, which is 3. In the hundreds place, again, there is no hundreds digit in 436, so we take the digit from 86639, which is 6. For the thousands place, we subtract 4 from 8, resulting in 4. In the ten thousands place, we subtract 3 from 6, giving us 3. Finally, in the hundred thousands place, we subtract 4 from 8, which equals 4. Combining all these results, we get the final answer of 86203.