Recall that the area of a circle can be determined by the formula pi * r(squared). Since we are given the diameter, we can divide it by 2, giving us the radius. 10 / 2 = 5 Now that we have all of our values, we substitute them into the formula for area. 3.14 * 5(squared) This simplifies to 3.14 * 25 Which gives us 78.5 I hope that helps.