first simplify the equation by subtracting like terms (in this case):
12x - 5x = 7x
y = 7x - 2
Since you are finding the x, you must isolate the x. Do the opposite of PEMDAS.(Note: because there is a equal sign, what you do to one side, you do to the other)
Used show you have more than what is needed. Example is you need 6 slices of pizza for all your friends but have 7 slices you have more than is needed.