Rationalization method is to be used while solving sums like these
Rationalization factor for :
1) 1/√a ------> √a
2) a + √b -------> a - √b
3) a - √b ---------> a + √b
4) √a + √b ----------> √a - √b
5) √a - √b ------------> √a + √b

537 / √705
As seen in above Rationalization Methods we can use 1^st rule to solve the problem
Thus 537 / √705 is multiplied the rationalizing factor i.e. √705
To balance the extra added rationlizing factor we multiply the given ratio by √705 / √705
Thus the result of (537 / √705) * (√705 / √705) = (537 * √705) / 705
Thus 537 / √705 = (537 * √705) / 705 = 20.224590046604
Thus 537 / √705 = (537 * √705) / 705 = 20(round off to nearest integer)