If x is the missing number, then, based on the given statement, you can write:
2x + 4 = 12
In order to find the value for x, proceed as follow:
2x + 4 = 12 subtract 4 both sides and simplify
2x = 12 - 4
2x = 8 divide by 2 both sides
x = 8/2
x = 4
Hence, the number is 4