Solve for the positive value of x such that 3sqrt(x^2-4x+4)=16.

The 3 is the small number next to the sqrt sign.

if you cube both sides you get:

x^2-4x+4 = 4096

x^2 - 4x -4092 = 0

now use the quadratic formula:

http://www.purplemath.com/modules/quadform.htm

where
a=1
b=-4
c = -4092

let me know what you get