Explanation

x*sqrt(x*sqrt(x)) = x*(x^(3/2))^(1/2) = x^(7/4); taking the 14th root gives x^(7/56) = x^(1/8). Thus m = 1/8 - option (A). Checking: (x^(1/8))^14 = x^(14/8) = x^(7/4), which matches x multiplied by the square root of x^(3/2).