You can put this solution on YOUR website! Lets look at: you can only multiply the radicals with the radicals; and the coefficients with the coefficients (if something has an exponent of (1/2), it is the same as that number in the square root!
5(45x^3y^2)^(1/2)*(5x)^(1/2)
5(5*3*3*x*x*x*y*y)^(1/2)*(5x)^(1/2)
((5)(3)(x)(y))(5x)^(1/2)*(5x)^(1/2)
15xy(5x)^(1/2)*(5x)^(1/2)
15xy(25x^2)^(1/2)
75(x^2)y