there is a rectangle that has half a circle on top.. height is 3ft and width is 4.2 ft.. the question is about how many feet of glass will he need to pirchase

Since the half circle is on top of the rectangle, the width of the rectangle is equal to the diameter of the half circle. In order to find how much glass we need, we need to find the area. The area of the rectangle is length times width, 4.2 * 3 = 12.6. Now to find the area of the half circle. Let's find the area of a full circle with the same diameter and then half it so it is the area of the half circle. I hope that makes sense. The area of a circle is radius squared times pi (3.14), r^2 * 3.14. The radius of the circle is half of the diameter so 4.2/2=2.1 = radius.       2.1^2 = 4.41. 4.41 * 3.14 =   13.8474. Now this is the area of a full circle, not a half circle. 13.8474/2 = 6.9237 simplified as 6.9. Add the two areas together. 12.6 + 6.9 = 19.5. You may need to round it up to a digit without decimals. Since the width and height are in feet, the total amount of glass needed is 20 sqft or 20 ft^2. I hope this helps.