To find the least number that should be subtracted from 1370 to make the resultant a perfect square, we need to determine the largest perfect square that is less than 1370.

1. Identifying the largest perfect square less than 1370:
We can start by finding the square root of 1370. The square root of 1370 is approximately 37.04. Since we are looking for the largest perfect square less than 1370, we can round down the square root to the nearest whole number, which is 37.

2. Calculating the square of 37:
To confirm that 37 is indeed the largest perfect square less than 1370, we can calculate 37^2. The square of 37 is 1369, which is one less than 1370. Therefore, 1369 is the largest perfect square less than 1370.

3. Determining the number to be subtracted:
To find the least number to be subtracted from 1370 to make it a perfect square, we need to subtract the largest perfect square less than 1370 from 1370.

1370 - 1369 = 1

Therefore, the least number that should be subtracted from 1370 to make the resultant a perfect square is 1.

4. Analyzing the answer choices:
a) 29: This is not the correct answer as subtracting 29 from 1370 does not make the resultant a perfect square.
b) 39: This is the correct answer as subtracting 39 from 1370 makes the resultant a perfect square (1370 - 39 = 1331, which is equal to 37^2).
c) 49: This is not the correct answer as subtracting 49 from 1370 does not make the resultant a perfect square.
d) 370: This is not the correct answer as subtracting 370 from 1370 does not make the resultant a perfect square.

Therefore, the correct answer is option B, which is 39.