Hi, could I have step-by-step guidance for this problem? Thank you in advance!

Mr. Wilson (in the interest of sustainability ) digs a hole in his garden 50 cm deep. Over a period of time he fills it to the top with leftover organic material. As time passes the lower layers of compost pack down more tightly, and thus have a higher density than the upper layers. One day Rob measures the density of the compost at various depths. He also estimates the cross-sectional areas of the compost heap at the corresponding depths. Here are his results: Depth (cm) Density (8 / cm' ) Area (cm2 ) 0 0.7 10,000 10 0.9 9,000 30 1.2 8,000 40 1.6 4,000 50 2.2 1,000 Use 4 trapezia to calculate the approximate number of kilograms of compost Rob has in the heap. What is the average density of the compost in the heap