What you want to do here is plug 2 in for x. when a question asks you to evaluate a certain equation at a certain number, it's just asking you to plug the value in for your variable. i'm assuming that 12x + 8 is meant to be set over 4 as a fraction.
(12(2) + 8)/4 ... figure out the top first. 12*2 = 24, 24 + 8 = 32.