Waec Model Questions Vol1 2017 Geography Question 26

A volcano erupts and releases ash that settles uniformly over the surrounding area. Agricultural land can tolerate at most 5 cm of ash thickness. The ash thickness T (in cm) at a distance d (km) from the volcano follows T = k / d². At a monitoring station 20 km from the volcano, the measured ash thickness is 2 cm. A town, shaped as a circle of radius 7 km, is located with its centre 15 km east of the volcano. Assuming 60 % of the town's area is agricultural land, determine (a) the minimum distance from the volcano within which ash thickness exceeds the safe limit, and (b) the percentage of the town's agricultural land that lies within this unsafe zone. Give the distance to one decimal place (km) and the percentage to the nearest whole percent.