Since 1A claims that the diagram is of a square, you can easily find the perimeter by multiplying just one side by 4, because the definition of a square says that all of its four sides are equal in length.
Take the left side, x and 4, and add them together, because both of these lengths add up to form the side of the square. You have found one side of the square, x + 4. Now multiply this side by 4 for the perimeter.
Perimeter is the length all around the figure, and since a square has 4 sides you would multiply one side by 4 to find the perimeter.
4(x + 4) is your expression for the perimeter of the square. You could probably solve 1B and 1C by substituting in 3 and 5 for x in the equation I've given you :)