7√3 + 2√27 - √75 = 7√3 + 2√(93) - √(253)
= 7√3 + 2*3√3 - 5√3
= 7√3 + 6√3 - 5√3
= 8√3

2√7 √21 = 2√(721) = 2√147 = 2√(493) = 27√3 = 14√3

(2√2 - √50) √2 = 2√2√2 - √50√2 = 22 - √100 = 4 - 10 = -6

(4√80 - √125) : √5 = 4√(165) - √25 = 44√5 - 5 = 16√5 - 5

6√х - (2/3)√9х + 10√х/4 = 6√x - 2√(9x) + 10√x/4 = 6√x - 6√x + (10/4)√x = 6√x - 6√x + 2.5√x = 2.5√x

(√a√b + √b) : √b = √(ab)/√b + √b = √a + √b