The following figure (not to scale) shows a catchment (Q, S, U, T, Q) and adjoining raingauge stations P, Q, R, S, U, V. Due to a storm, rainfall depths were recorded as follows:
- P = 20 mm, Q = 25 mm, R = 30 mm, S = 15 mm, U = 22 mm, V = 18 mm.
The corresponding mean rainfall over the catchment using Thiessen polygon method is ............... (in mm, rounded off to two decimal places).
