p = x^2 + 2y 3 ;     q = 3x + y^21 ; Solve[ {p, q }, {x, y}]

{{x1/3 (9/(1/3 (4 - (154 2^(2/3))/(1247 + 27 12153^(1/2))^(1/3) + (2 (1247 + 27 12153^ ... /3 (4 - (154 2^(2/3))/(1247 + 27 12153^(1/2))^(1/3) + (2 (1247 + 27 12153^(1/2)))^(1/3)))^(1/2))}}


Created by Mathematica  (December 21, 2007)