Look at the remaining trees and the number of oranges they produced.
41790 oranges were produced.
Each tree produced 210 oranges.
The number of remaining trees is 41790/210.
Originally, there we 5 more trees.
The original number of trees is 41790/210 + 5
The equation is
t = 41790/210 + 5
Now we evaluate the right side.
t = 199 + 5
t = 204
The original number of orange trees is 204,