Question 192
note that 18=9*2, 50 = 25*2, 72 = 36*2. 9, 25 and 36 are squares of 3, 5 and 6 can be taken out of squar root as 3, 5, and 6 respectively. So, you get 

= 3.&#8730;18 - &#8730;50 + 3&#8730;72 = 3.3&#8730;2 - 5&#8730;2 + 6.2&#8730;2 = &#8730;2( 9 - 5 + 12)

= 16&#8730;2