reorder tu 6*sqrt(125)-sqrt(98) -6*sqrt(72) -5*sqrt(20)
125=5*25, so sqrt(125) become 5*sqrt(5) & 6*sqrt(125)=30*sqrt(5)
98=2*49, so sqrt(98) become 7*sqrt(2)
72=2*36, so sqrt(72)=6*sqrt(2)...-6*sqrt(72)=-36*sqrt(2)
20=4*5, so sqrt(20)=2*sqrt(5)...-5*sqrt(20)=-5*4*sqrt(5)
sum=30*sqrt(5)-20*sqrt(5) -7*sqrt(2) -36*sqrt(2)
=10*sqrt(5) -43*sqrt(2)