the first one x^2 - 16 is a difference of squares question

if you are able to square root both terms AND they are being subtracted from one another you can write it like this

x^2 - 16 = (x - 4)(x + 4), and x = 4, x = -4

for the cubics (the ones that have 3rd degree or highest power is 3, ex the last in the list), check out this video

Solving cubics

you could use the calculator to graph the functions and then see if it tells you the X intercepts

its probably easier to not use the calc though hehe