Stephen H. answered 01/13/20
Tutor of Math, Physics and Engineering ... available online
sqrt(5x+6)=3+sqrt(x+3)
5x+6=9+6sqrt(x+3)+x+3
4x-6=6sqrt(x+3)
16x^2-48x+36=36x+108
16x^2-84x-72=0 .... x=6, -.75
sub x=6 ... sqrt(5*6+6)=3+sqrt(6+3) ... 6=6, thus x=6 is a real solution
sub x=-.75 ... sqrt(-5*.75+6)=3+sqrt(-.75+3) ... sqrt(2.25)=3+sqrt(2.25) is not true ... thus x=-.75 is not real