To add fractions, we need to find a common denominator.

For the first expression, 3/4 + 5/18:

First, find the least common multiple (LCM) of 4 and 18, which is 36.

Now, rewrite the fractions with the common denominator of 36:

3/4 = 27/36
5/18 = 10/36

Now, add the fractions:

27/36 + 10/36 = 37/36

Therefore, 3/4 + 5/18 = 37/36

For the second expression, 4/210 + 5/140:

First, find the least common multiple (LCM) of 210 and 140, which is 420.

Now, rewrite the fractions with the common denominator of 420:

4/210 = 8/420
5/140 = 15/420

Now, add the fractions:

8/420 + 15/420 = 23/420

Therefore, 4/210 + 5/140 = 23/420