you would subtract the "x" from four and move it to the x squared. so then the equation would read
x^3+4-16=0
once it reads that combine the 4 and 16 (you could have done that in the last step too) so then it will read
x^3-12=0
then you just have to figure out what to the power of three equals 12 so that when you subtract you get 0.
