Ta có : 

a.

$B=\sqrt{16x+16}-\sqrt{9x+9}+\sqrt{4x+4}+\sqrt{x+1}$

$B=\sqrt{16(x+1)}-\sqrt{9(x+1)}+\sqrt{4(x+1)}+\sqrt{x+1}$

$B=4\sqrt{x+1}-3\sqrt{x+1}+2\sqrt{x+1}+\sqrt{x+1}$

$B=4\sqrt{x+1}$

Vậy $B=4\sqrt{x+1}$ .

b.  

Để B = 16  <=> $4\sqrt{x+1}=16$

<=>  $\sqrt{x+1}=4$

<=>  $\left\{\begin{matrix}4\geq 0 & \\ x+1=4^{2} & \end{matrix}\right.<=> x=15$

Vậy x = 15 thì B = 16 .