The little three above the 2 represents how many times you should multiply 2 to itself.
2³ = 8, because it's the same as 2 × 2 × 2 (notice how 2 has been multiplied by 2, 3 times).
So now that you know 2³ = 8, you just need to add 4, which is just 8 + 4 = 12.
