The quadrilateral you're describing sounds like a rectangle because of the right angle and equal opposite sides.
(a) The area of a rectangle is found by multiplying the length by the width. So, 4in*12in = 48 square inches.
(b) The perimeter is found by adding all sides. So, 4in + 5in + 12in + 5in = 26 inches.
So, the area is 48 square inches and the perimeter is 26 inches. Geometry is quite fascinating, isn't it?