a question about tangent lines and slopes

the question is:

Find the points on the graph of y = x ^ (3/2) - x ^ (1/2) at which the tangent line is parallel to the line y - x = 3.

i have derived the first function to find the tangent line then i have derived it again to find it's slope, then derived the second function to get it's slope, then i have set the first slope = the second slope anyway this is what i got lastly:

(3/4) x ^ (-1/2) + (1/4) x ^ (-3/2) = 1

i could not get the value of x from this equation.is there any formula that will get me the value of x like the quadratic formula?