The linear approximation to [tex]f(x)[/tex] near [tex]x=16[/tex] is
[tex]L(x)=f(16)+f'(16)(x-16)[/tex]
We have
[tex]f(x)=\sqrt x\implies f(16)=4[/tex]
[tex]f'(x)=\dfrac1{2\sqrt x}\implies f'(16)=\dfrac18[/tex]
[tex]\implies L(x)=4+\dfrac18(x-16)=\dfrac x8+2[/tex]
Then
[tex]f(16.2)\approx L(16.2)\iff\sqrt{16.2}\approx\dfrac{16.2}8+2[/tex]
[tex]\implies\boxed{\sqrt{16.2}\approx4.025=\dfrac{161}{40}}[/tex]