√(8x + 1) = 5 ---> (√(8x + 1)² = 5² ---> 8x + 1 = 25 ---> 8x = 24 ---> x = 2  
√(5x - 4) = 6 ---> (√5x - 4)² = 6² ---> 5x -4 = 36 ---> 5x = 40 ---> x = 8  
√(7x - 3) - 2 = 0 ---> (√(7x - 3))² = 2² ---> 7x - 3 = 4 ---> x = 1
√(5x²) - 3x = 2x ---> √(5x²) = 5x (x ≥ 0) ---> x · √5 = 5x ---> √5 ≠ 5 - given equation does not have any solutions.
√(5x² - 3x) = 2x (x ≥ 0) ---> (√(5x² -3x))² = (2x)² ---> 5x² -3x = 4x² --->
(5x² - 4x²) -3x = 0 ---> x² -3x = 0 ---> x(x - 3) = 0 ---> x₁ = 0 , x₂ = 3

I show you how to do the first. You can try the following problems.

√(8x+1) = 5

Square both sides,

8x+1 = 25

x = 3 <==Answer