Answer is 46. But why should we complicate the calculation by considering First two trees and then calculating for the rest?
Let n = number of trees
n-1 = number of Gaps between n trees
n (1) + (n-1) 16 = 3/8 (1000).
=> n = 23
Ans is 23*2= 46.
Total distance between first two trees (on any side) = 18m.
Subsequent trees will be at a distance of 17m.
If there are a total of n trees beyond the first two trees then
18 + 17n = (3/8)*1000 = 375
or, n = 21
Hence, there are 21 + 2 = 23 trees on one side of the road and 46 trees on both sides of the road.