Me ! i can't figure out how to solve that

X^2  +    9x^2
               =   16
         (x + 3)^2  

multiply each term by (x + 3)^2:-

x^2(x + 3)^2 + 9x^2 = 16(x + 3)^2

x^2( x^2 + 6x + 9) + 9x^2 = 16x^2 + 96x + 144
x^4 + 6x^3 + 18x^2 = 16x^2 + 96x + 144
x^4 + 6x^3 + 2x^2 - 96x - 144 = 0

This is difficult to solve algebraically so I drew a graph There are 2 real roots
x =  -1.65 and x = 3.65 to nearest hundredth