[R] question about ways to solve nonlinear system

[Leite,Walter]

Dear R users


I am trying to write an R function to solve for a,b,c in the following
system of equations, given any value of x1, x2 and x3:
b^2 + 6*b*a + 2*c^2 + 15*a^2 = x1
2*c*(b^2 + 24*b*a + 105*a^2 + 2) = x2
24*(b*a + c^2*(1 + b^2 + 28*b*a) + a*(12 + 48 *b*a + 141*c^2 + 225*a^2))
=x3

Could you give me suggestions about which R function(s) I can use to
solve this problem and how I should use these functions? 
Thank you very much for your assistance,

Walter Leite