Question

simplify by combining like terms:

x sqrt(18) - 3 sqrt(8x)sqrd

If <sqrt(8x)sqrd> means [sqrt(8x)]^2, then that also equals 8x. So
x sqrt(18) - 3 sqrt(8x)sqrd
= x[sqrt(9*2)-3*8]
= 3x(sqrt 2 -3