If you were to graph these 2 functions, you would see that they intersect at the following points. (-3,0) and (0,6) so these would be your solutions
You could also solve this algebraically using substitution:
2x + 6 = x² + 5x + 6
0 = x² + 5x + 6 - 2x - 6
0 = x² + 3x
0 = x(x + 3) which implies x = 0 and x = -3 you can now plug these values in for x in the linear function to find the corresponding y coordinates.
Hope this helps