Do the Equations X² + Y²s + Yt² =13 and Y²

Do the equations x² + y²s + yt² =13 and y² + x²s + xt² = 9 define s and t as functions of x and y near the point (x, y, s, t) = (1, 2, 1, -2) ? If so, find at that point.

A) 2
B) 1
C) 0
D) -2
E) The equations do not define s and t as functions of x and y near the given point.