It depends on what it is meant to be equivalent to!
4x
12
It is equivalent to: 6x^2 -8x -8
x^2 +8x -9 is equivalent to (x+9)(x-1) when factored
5
8(x+5) is equivalent to 8x+40
It is equivalent to: 32x^2 +88x +21
80*8.8 800*0.88 8000*0.088
16
It is equivalent to: 3x+6+5 = 3x+11
25 percent of 8x = 2x25% of 8x= 25% * 8x= 0.25 * 8x= 2x