Solve for Real Roots $$2 x ^ { 1 / 2 } - 11 x ^ { 1 / 4 } - 21 = 0$$

Multiple Choice

Solve for real roots.
- $$2 x ^ { 1 / 2 } - 11 x ^ { 1 / 4 } - 21 = 0$$

A) $x = 2401$
B) $x = 7 , - \frac { 3 } { 2 }$
C) $x = 2401 , \frac { 81 } { 16 }$
D) $x = - 7 , - 3$