Question 136214
No, you need to solve your equation for x, and then substitute 6 for N.


You don't say where x goes in your formula, but I'm going to presume that it goes with the 4 and that both the 16 and the 4 are under the radical, like this:


{{{N=sqrt(16+4x)}}}


Square both sides:
{{{N^2=16+4x}}}
{{{4x=N^2-16}}}
{{{x=(N^2/4)-4}}}


Now substitute 6 for N and do the arithmetic.