The field is planted with grass, with 2.5 m uncovered on its sides.
The field is shown in the given figure.
Thus, we have;
Length of the area planted with grass = 35-(2.5 + 2.5) = 35-5 = 30 m
Width of the area planted with grass = 18-(2.5+2.5) = 18-5 = 13 m
Area of the rectangular region planted with grass = 30 x 13 = 390 sq m.