8x-49^2-16
because -7x(4+7x) is broken down to
-7x*4 = -28x
and
-7x*7x= -49x^2 the square root is because x*x= x^2
then you do the second part which is
-8(2-4x) and again you break it down
-8*2=-16
-8*-4x=36x
so now you have
-28x-49x^2-16+36x
and when you simplify you get
8x-49^2-16