A wooden plant accumulates 10 mg kg−1 of 14C during its life span. A fossil of this plant was discovered and contains 2.5 mg kg−1 of 14C. The age of this fossil at the time of discovery is __________ years (rounded off to the nearest integer).
(Use 5730 years as half-life of 14C)
Enter numerical value using the virtual keypad. Round off where necessary.