if you look closely at this expression you'll notice that each polynomial is almost all different except for 3x and 8x because they share the same unknown variable. you couldn't choose 8 because that is just a whole number and all the other numbers contain a variable. and you couldn't choose 3y because y only affects the 3 in this expression whereas x affects 3x and 8x therefore the right answer is 3x and 8x which are the like terms.
